Solving time: 62:19

I found this a very easy solve. Indeed this is probably a record time for a jumbo for me, almost under the hour.

There does appear to be a mistake at 39a, however. The setter seems not to know his financial slang. A pony is £25 and a monkey is £500, supposedly from the design on old rupee notes of those denominations, dating from the time of the British Empire in India. Here, though, it has been clued as 'a thousand in cash'. I'm completely wrong (as usual) as fathippy2 has pointed out. The clue is cleverer than I gave it credit for.

cd = cryptic def., dd = double def., rev = reversal, homophones are written in quotes, anagrams as (--)*, and removals like this

Across
1	PA + PA + W
4	CELEBRATOR = (REBEL + ACTOR)*
9	B + LOWER
14	OLIVE DRAB = O + (BARD + EVIL) rev - I didn't know the colour, but it was easy enough to deduce from the wordplay.
15	HEART-BREAKING - HEART = (EARTH)*. I'm not convinced the wordplay quite works in the strictest sense, but it was clear enough.
16	SO-AND-SO - dd
17	REMaINDERS = 'couple of tokens' is the definition. There's a lot of clue here for not much wordplay.
18	NEEDY = ED in YEN rev
19	PERSONAL STEREO = (SPOONER'S REAL)* about TE
22	RED + CARD
25	CHEW THE FAT = CAT (spiteful woman) about HEW (to cut) + THE (article) + F (female)
27	MARK + kickS + MAN'S + HIP
30	TA + TAR
31	GO TO TOWN = TOp x2 in GOWN
32	C + HANDLER - Raymond is of course the author. The boxer in question is of the canine variety, so this is a dog handler.
35	HERmITAGE
36	PEARMAIN = PEN (shut up) about A + RM (jolly, i.e. sailor) + AI (excellent)
37	ALBUM = LA rev + BUM
39	GREASE MONKEY = "GREECE" + MONKEY - a 'monkey' in London slang is £500, and not £1000 as this clue seems to imply. No, it's K (a thousand) in MONEY (cash) - thanks to fathippy2 for pointing this out, and my humble apologies to the setter.
41	POLYHEDRON = (HER OLD PONY)*
43	SHOTGUN = bayoneT in SHOGUN
45	PLAIN CHOCOLATE = (H + LOCATION PLACE)*
48	MOI + RA
49	RECEPTION = DECEPTION (fraud) with Democrat replaced by Republican - 'party' is the definition.
51	SIGN + O + RE
53	GENT + IAN + VIOLET - Not something I had heard of, but easy enough to work out from the checkers.
54	SMALL-TIME = EMITS rev about MALL
55	PAL + TRY
56	INCANDESCE = (NICE DANCES)*
57	GET IT = TIT + EG all rev
Down
1	PROUST = PRO (for) + T (short time) all about US (America)
2	PRIVATE SECTOR = PRIVATE (one soldier) + OR (Operational Reserve, i.e. other soldiers) all about SECT (religious group)
3	WIELD = knifE in WILD
4	CARTOON = CON about (ART + O)
5	LIBERAL PARTY = (TERRIBLY + A PAL)*
6	BE(H)E + MOTH
7	A + GAIN
8	ON THE ROCKS - dd
10	LE(ARNE)D
11	WHITEWASH = WASH (stand up, as in 'that explanation just won't wash') under WHITE (chess player)
12	dRUG + BY
13	TRISTRAM SHANDY = (ARTISTRY HAND)* about MS - Why is this novel so popular with setters? I must have seen it crop up 5 or 6 times over the years.
20	SATURATES = R in (USA STATE)*
21	RO(A)D + WORK
23	DEPARTMENT = DEPORTMENT with O changed to A
24	SCOTCH + EG + GarageS
26	ENGAGEMENT RING - cd
28	NONPAREIL = NIL (nothing) about ON (leg, side in cricket) + PARE (cut)
29	ST HELENs + A
33	LIBERATIONIST = (LIAISON + BITTER)*
34	SAXOPHONISTS = (SNAPSHOTS I)* about (X + O)
38	IN + S(P)ECTION
40	EMOTIONAL = TOME rev + I + ON + A + Lady-killer
42	ENLISTED = LISTEn (almost pay attention) in the END (finally?)
44	niGht + LAZIER
46	CAS(CAD)E - that's suit as in lawsuit
47	DEFECT - dd
48	MUG + UP
50	PALMA = (A + MAP) rev about L
52	GUn + LAG