I started quickly, picking the proverbial low-hanging fruit. Things changed about halfway through, and the rest was a struggle. The obscurity and artistry of many clues had me doubting answers even when I saw them.

LOI was 19ac, where I was thinking “sexy” rather than “stolen”. Second last was 2dn, where I don’t know quite how to categorise the definition. Clues like 24ac had me hesitating to write the answer in when I saw it, until I had all the checkers. The wordplay in 18dn also rates a mention for being particularly obscure. Thanks to the setter for a very enjoyable puzzle!

Clues are in blue, with definitions underlined. Answers are in BOLD CAPS, then wordplay. (ABC*) means 'anagram of ABC'. Deletions are in [square brackets].

On edit: thanks to Phil Jordan for pointing out the floral Nina at 3dn+21dn, and 6dn+18dn. See the first comment!

Across
1 Morally corrupt equivalent of ten depressions? (8)
DECADENT: count these depressions with me: mono-dent, duo-dent, … deca-dent.

5 Result of laying hold firmly (6)
CLUTCH: double definition, to do with eggs or grasping.

10 Drunk again, ale’s numbing pain (9)
ANALGESIA: “drunk” (anagram) of (AGAIN ALES*).

11 Key discussion curtailed after six (5)
VITAL: VI (six), TAL[k] “curtailed”.

12 Seconds from parching, planters use borehole as well (4)
ALSO: an answer spelled out by the second letter of each word.

13 Field expertise reduced amount of green growth (9)
LEAFINESS: LEA (field), FINESS[e] (expertise, “reduced”).

15 Pause to rest, stopping the man endlessly busy working (10)
HESITATION: SIT (rest), “stopping” HE (the man), AT I[t] (busy, “endlessly”), ON (working). One of the clues I hesitated (yes, hesitated) to write in until I had the crossing letters to confirm that it fitted.

17 Something to drive about India without success (4)
VAIN: VAN around I for India. Definition as in, “the search was vain”.

19 Chews over new leaves — hot stuff? (4)
SWAG: SWAG=G[n]AWS (chews), “over” (i.e. backwards) and without N for new.

20 Money to protect king and knight in great urban moves? (5,5)
BREAK DANCE: BREAD (money) “protecting” K (king), and N (knight) in ACE.

22 Originally eaten in Mexico, not a thing with mostly cold filling? (9)
ENCHILADA: E (“originally” Eaten), followed by CHIL[l] (“mostly” cold) “filling” NADA (in Mexico, not a thing). And, the whole clue is the definition. Definitely, high art.

24 Told office to exclude British — for their neighbours’ funding? (4)
EURO: sounds like (“told”) BUREAU, with the sound of B for British excluded. As noted, I waited for both helpers before putting this in!

26 Literarily, it’s going to weave (5)
TWILL: ‘twill with an apostrophe being a literary contraction of “it will”.

27 Piece of meat where rest can be had in dish before main course (9)
ENTRECOTE: COT (where rest can be had) in ENTRÉE (dish before main course).

28 Deny women’s being released from old prison (6)
NEGATE: release the W from NEWGATE.

29 Being There, for which acting needs time given over to Sellers’ lead (8)
PRESENCE: PRETENCE (acting), with the T changed to an S.

Down
1 Daughters without refinement are attractive? (4)
DRAW: D (daughters), RAW (without refinement).

2 Nurse Carol naturally enters senior partner’s practice? (6-9)
CRADLE SNATCHING: CRADLE (nurse), NATCH (naturally) in SING (carol). A particularly cryptic definition, I thought, referring to an old man perhaps (the senior partner), taking up with a young woman.

3 Tidy black-clad punk getting around to canine (8)
DOGTOOTH: DO (tidy), GOTH around TO.

4 Twangy part for musician, as always (5)
NASAL: hidden answer (indicated by “part”).

6 See that vessel where hippies got it on (4-2)
LOVE-IN: LO (see that), VEIN (vessel).

7 Month Robert worked round old queen like a natural (2,3,6,4)
TO THE MANNER BORN: anagram (“worked”) of (MONTH ROBERT*), around ANNE. I remember the Penelope Keith series To the Manor Born so well, the actual answer momentarily looked like a mis-spelling.

8 List containing lines informed gang member (5,5)
HELL’S ANGEL: HEEL (list), “containing” LL (lines) and SANG (informed).

9 Answer Scottish island charge after mounting, baseless fear (8)
PARANOIA: A (answer), IONA (island), RAP (charge, as in “beat the rap”), all reversed (“mounting”).

14 Bust in Paris, our rising British author (10)
CHESTERTON: CHEST (bust), ERTON=NOTRE (in Paris, “our”; “rising”).

16 Cut yarn number in loom (8)
THREATEN: THREA[d] (“cut” yarn), TEN (number).

18 Unemployment I should lower, ending four points up (8)
IDLENESS: I’D (I should), LE-NESS = LE-SSEN (lower), with the last four letters reversed (“points up”).

21 Shade from screen infused with exotic oil (6)
VIOLET: VET (screen) “infused with” an anagram (of (“exotic”) (OIL*).

23 Famous dancer doesn’t have heart or foot moving (5)
ASTIR: the dancer was AST[a]IR[e], trimmed as instructed.

25 Unimpressive million in advance, once (4)
MERE: M (million), ERE (in advance).

Crikey, these come around quickly when you have a couple of bank holidays in quick succession so I'm afraid you've got me again.

So here we have another puzzle with a bit of a popular music undercurrent, deliberate or otherwise.  I'll point out the references as we go through.

This wasn't too taxing, taking about 40 minutes all told, but I did need to cheat to get my LOI, ALIQUOT.  First in was LAM as my eye was drawn to the 3-letter light.

Clues are in blue with the definition undelined.  Anagram indicators are in bold italics.

Notation:

DD: Double definition

CD: Cryptic definition

DDCDH: DD/CD hybrid where a straight definition is combined with a cryptic hint.

&Lit:  "all in one" where the entire clue is both definition and wordplay.

(fodder)* denotes an anagram of the letters in the brackets.

Rounded brackets are also used to add further clarity

Squiggly brackets {} indicate parts of a word not used

Deletions are struck out

Square brackets [] expand an abbreviation or shortening like N[orth]

Across
1	Light rain: Jack sheltering in hollow that’s welcoming (10)
	HOSPITABLE - SPIT and A[ble] S[eaman] sheltering in HOLE
6	Ignorant group is taken in by hacker (4,3,5)
	NONE THE WISER - NONET, then IS in HEWER.  Album by The Rifles, one of my favourite bands.
14	Animal has tail at first, one to cut back (7)
	POLECAT - teversal of T{ail}, ACE, LOP
15	Source of wealth around old church of a distant epoch (7)
	MIOCENE - MINE around O[ld] C[hurch] [of] E[ngland]
16	Emperor carrying on with unknown character — that's anything but love? (3-4)
	NON-ZERO - NERO around ON, Z
17	Mock a noted conclusion (4)
	CODA - COD, A. Patchy Led Zeppelin album of outtakes.
18	Discussion involving Tory — amazing (6)
	CONFAB - CON[servative] FAB[ulous].  One of those words that "normal" people (i.e. not us) say wrong ("conflab").
20	Attentive chap from East Timor? (8)
	DILIGENT - A gentleman from Dili, the capital of East Timor (no, me neither) would be a DILI GENT.
24	Now partner has ruined everything, after happening to cause upset (5,1,7,2,3,5)
	THROW A SPANNER IN THE WORKS -
25	Girl has put short stockings on — hallelujah! (7)
	HOSANNA - HOSe, ANNA
26	Friend a nuisance in European city (8)
	BUDAPEST - BUD, A, PEST
27	In a fine spray deodorant initially contained (6)
	AMIDST - A MIST around D{eodorant}.  One of those pesky hard to spot definitions.
29	Thickness not diminished, roughly about right (5,9)
	THIRD DIMENSION - (not diminished)* around R[ight]
31	Pernicious lady about to steal fella's heart (8)
	DAMNABLE - DAME around NAB {fe}L{la}
34	Interesting it's coming together (8)
	ENGAGING - DD
36	Turning scarlet, the sour dessert (9,5)
	CHARLOTTE RUSSE - (scarlet the sour)*
39	About to marry deadwood (6)
	REFUSE - RE, FUSE
41	Stairs including an opening (8)
	FANLIGHT - AN in FLIGHT
43	Anxious over cracks in heater returning (7)
	NERVOUS - (over)* in a reversal of SUN
46	Having saved little US cash, silly granddad, he wed nan, getting severely punished (6,5,3,9)
	HANGED DRAWN AND QUARTERED - (granddad he wed nan)* around QUARTER.  The statutory penalty for high treason, but only for men.  Women got off lightly and were burned at the stake.
47	Quibble darling? Move well back! (8)
	PETTIFOG - PET (darling in the North East for instance) then a reversal of GO FIT
48	State having twisted story, journalist going into it (6)
	SWEDEN - ED[itor] in NEWS reversed
49	Suspect image for recollection, provided in terrible case (1-3)
	E-FIT - reversal of IF in T{erribl}E
53	Equal measure in a tumbler originally containing reduced drink (7)
	ALIQUOT - A T{umbler} around LIQUOr.  I didn't know the word and couldn't think of a shortened drink to fit the middle bit so had to resort to aids.
54	Mineral container one returned, awaiting delivery (2,5)
	IN UTERO - reversal of ORE, TUN, I and Nirvana's final studio album.
56	Finally abandoning south for north, then a southern US city (7)
	ATLANTA - AT LAST A with S[outh] replaced by N[orth].  Double bluff from the setter - an experienced solver's spidey senses would normally tell them that "southern US city" meant S then a Northern, Western or Eastern US City, or even SUS and a city elsewhere in t'world.
57	Drink in exciting bars, say? (3,9)
	HOT CHOCOLATE - HOT, CHOCOLATE, pretty naff "soul" band.
58	Sweet wine no great shakes? (10)
	AFTERSHOCK - AFTERS, HOCK.  Is this a chestnut yet?

Down
1	After trip, stop game (9)
	HOPSCOTCH - HOP (presumably as in hopping across the channel to buy some cheap lager) + SCOTCH
2	Saucy thing beginning to strip — a boy doing otherwise? (5,8)
	SALAD DRESSING - S{trip}, A LAD DRESSING (i.e. not stripping)
3	Island, a short distance (4)
	INCH - DD
4	Sat on Titanic so agitated, prepare for a battle! (6,8)
	ACTION STATIONS - (sat on Titanic so)*.  I think that's one of the things my talking Action Man used to say.
5	In Nepal, a meteor hit (3)
	LAM - hidden
7	Original ode's first up for poet (4)
	OWEN - reversal of NEW O{de}.  Wilfred presumably, unless Michael has started writing football sonnets.
8	One seeing English tree, it overlooking cape (10)
	EYEWITNESS - E[nglish], YEW, IT, NESS
9	Party bringing leaders of neighbouring nations into prominence (3,5)
	HEN NIGHT - N{eighbouring} N{ations} in HEIGHT
10	Extraordinary female made up new word where Arabic spoken (6,5)
	WONDER WOMAN - (new word)* + OMAN
11	Protected pigs ultimately led there to be slaughtered (9)
	SHELTERED - {pig}S + (led there)*
12	Little jumper, fine top (4)
	ROOF - ROO, F[ine]
13	Together in neatly arranged houses (8)
	COMBINED - IN "housed by" COMBED
19	Lit up at dinnertime, darling goes in to eat (8)
	FLAMBEED - LAMB in FEED
21	Identical daughter gets hold of bandage finally for wound (6)
	TWINED - TWIN D[aughter] around {bandag}E
22	Inspired by rock, style of music to perform — that's for dropouts? (4,4)
	TRAP DOOR - TOR around RAP, DO
23	Weariest when travelling, in a kind of way (2,2,4)
	AS IT WERE - (weariest)*
28	Mean knock? (7,7)
	BATTING AVERAGE - Cricketing CD.  A knock is an innings and a mean is an average.
29	Ecclesiastical governors the chief enemy in conclusion (8)
	THEARCHY -THE ARCH {enem}Y
30	English town succeeded before the French city (2,6)
	ST HELENS - S[ucceeded], THE LENS
32	Singer ending in club like so, for enjoyable party (5,8)
	BASSO PROFUNDO - {clu}B, AS, SO, PRO, FUN, DO
33	Match fit, perhaps, though no start in store (8)
	BOUTIQUE - BOUT, pIQUE.  At least I think that's how it works.  You can have a fit of pique but fit doesn't mean pique.  Any better suggestions?
35	Essay on wheat, book totally factual (6,5)
	GOSPEL TRUTH - GO, SPELT, RUTH
37	Curiosity — artist needs it to read between the lines? (6)
	RARITY - R[oyal] A[cademician] then IT in R[ailwa]Y
38	Hot stuff, with nothing in court case being vulgar (10)
	LAVATORIAL - LAVA then O in TRIAL
40	Details I infer scattered around page on book (4,5)
	FINE PRINT - (I infer)* around P[age] then N[ew] T[estament]
42	Criminal comedian admitting beaten, finally (8)
	GANGSTER - GAGSTER around {beate}N
44	Distract team with song (9)
	SIDETRACK - SIDE, TRACK.  I recently bought a Bluetooth turntable so some of my old vinyl is getting an airing again.
45	A bit of water and a second, neither quite finding sea (8)
	ADRIATIC - A DRI{p} A TIC{k}.  Nice one.
50	Dish — or pot? (4)
	HASH - DD.  Corned beef or weed madam?
51	Sculptor's piece in pieces! (4)
	BUST - DD
52	Something more luxurious, cut (4)
	PLUS - PLUSh
55	A female with nothing up top? (3)
	OAF - A F[emale] under O, &Lit

This all seemed fairly straightforward, and straightforwardly fair, but wittily engaging and elegantly clued. I doubt if anyone will have had major problems.

This afternoon at an event remembering Jonas Mekas (1922–2019), I learned that the great patron saint of noncommercial film had stayed many times during the last five decades at the hotel La Louisiane in Paris… I regret to say that I returned to the States over a week ago, though it doesn’t seem nearly so long. The avatar now replacing the one from La Louisiane shows the foot of the stairs in my apartment building, with Art Deco runes written in light on the floor. I don’t recall ever having seen, or noticed, that before in all my 27 years here. It seemed a hopeful sign… That I'm posting another such picture has nothing to do with the fact that in 2018, as some of you are aware, a much shorter flight of stairs led to my downfall.

I do (nasargam)* like this, and italicize anagrinds in the clues.

ACROSS
1	Two short cuts to good health (4-4)
	CHIN-CHIN — Salut ! That’s either CHIN[-k] CHIN[-k] or (see the first comment) CHIN[-e] CHIN[-e]—what do you think? Cast your vote now!
5	A fake king’s in retreat (6)
	ASHRAM — A + S(R)HAM, R being “Rex,” “king”
9	Taking on family over claims it openly admits (8)
	NEPOTISM — Reverse (“over”) hidden
10	Benefits after wife gives birth (6)
	WHELPS — W(ife) + HELPS (“benefits”)
12	Worry as steed might bolt a lot (3,4,1,5)
	EAT LIKE A HORSE — EAT (“worry” ) + LIKE A HORSE (“as steed”). The surface sense of “bolt” here is not unrelated, in a punning way, to the word’s cryptic sense in 11.
14	My turn to keep quiet (4)
	GOSH — GO, “turn,” + SH, “keep quiet”
15	Writers’ articles still being reported (10)
	STATIONERY — Sounds like “stationary”
17	Table item about protective fabric before lunch? (6,4)
	NAPKIN RING — CD. (I looked too long for something else going on here.)
19	Instrument’s top broke, not every other part (4)
	OBOE — tOpBrOkE
22	Inmates’ chests whipped as punishments (13)
	CHASTISEMENTS — (Inmates’ chests)*
24	Sly person beginning to win artist’s support (6)
	WEASEL — W(in) + EASEL
25	One painting over wild animals’ shelters (4,4)
	MONA LISA — (ANIMALS)* with O(ver) taking refuge inside.
26	Moderately attractive (6)
	PRETTY — DD. (And the dullest clue in the bunch.)
27	Smother last bit of strudel in rum (8)
	STRANGLE — STRANG(L)E

DOWN
1	Data introduced to win over meeting (10)
	CONVERGENT — CONVER(GEN)T. Oxford says this sense of “gen” dates from the “Second World War (originally used in the armed services): perhaps from the first syllable of general information.”
2	Sort of mine not left by American force (7)
	IMPETUS — (-l)IMPET + US. A limpet mine is a time bomb attached magnetically to the hull of a ship.
3	Cold serving of beer beside a climbing plant (6)
	CATNIP — C + PINT,A<= (“climbing”)
4	Speak with vet before examining body (12)
	INSPECTORATE — ”Speak” is ORATE and “vet,” INSPECT” precedes it
6	Chess or alternative involving unknown lighter pieces (8)
	SCHERZOS — (Chess or)* entangling the unknown Z
7	Take over from priest always twirling robes (7)
	RELIEVE — EVER<= (“always twirliing”), with the ever-popular priest ELI dropping in
8	Tom’s cries sounded deliberate (4)
	MUSE — I hear a cat… (mews)
11	First photo’s a sprinter, given too much too soon (4,4,4)
	SHOT ONES BOLT — SHOT ONE is “First photo” and a (very well-known) sprinter is a certain Usain BOLT
13	An area of sci-fi advertisers rate (10)
	HYPERSPACE — HYPERS + PACE. We have hyperlinks to cyberspace, but hyperspace is not real, so far. Darn.
16	Tissue produced by soldier, upset during elegy (8)
	LIGAMENT — L(GI<=)AMENT
18	Wrap up season below Wolves? (7)
	PACKAGE — AGE is “season” and the PACK could be (DBE) a gang of wolves (sans the deceptive capitalization)
20	Singer able to fly flags (7)
	BUNTING — DD
21	Journalist’s left skewered by a horned beast (6)
	IMPALA — IMPAL[-ed, or “editor,” “journalist”] + A. My LOI, though the animal was obvious by that point. Did anyone else find this the hardest to parse?
23	Substitute seen putting feet up (4)
	SWAP — PAWS<=