If 'genuine intimate time' just means full physical intimacy, then yes it's almost entirely money, though as others have said there are exceptions.
It's a more interesting question if 'genuine intimate time' means sex that's deeply intimate in most of the ways the best unpaid civvy sex is. I.e. the lass acts like she genuinely desires you, is really keen for sex, responding like it's the best thing in the world, surrendering to you totally if she's the passive type, or if she's the active type, fucking you like she's desperate for the deepest possible connection.
This is normally the sort of experience money can't buy. (Except maybe in rare cases with a really good actress). But while looking after yourself is going to help, I'd agree looks & physique aren't that important either. Cos if they were myself & many other middle aged punters who are no oil painting wouldnt have had such experiences several times. These are the main reasons IMO:
1) Nature of the WG. As jimbobted said, it helps if the lass is that rare sort who seems to genuinely like sex for its own sake with lots of different random men. I think JonasG & myself both experienced this with Rose Thai - she was unbelievable keen as per our reviews.
2) 'Click' - if the punter doesnt has some chemistry with the WG, really keen sex is unlikely to happen.
3) Luck, timing & hormones.
I'd say no 3 is the most important. Women will sometimes be far keener for sex depending on where they are with their hormone cycle. I've seen this with civvy lasses, and with WGs, as I'm mostly a 'regular' GFE sort of punter who visits their fave many times. On most punts the sex I get from them is merely good, but every once in a while they are noticeably keener than normal both in how they act and physical signs like level of wetness and swelling of body parts. Almost certain it's not me acting different on those special times - more likely I've just been lucky with my timing.