Thank you Ejw - that's really helpful, as I was wondering if they'd just refuse. Definitely my best option when / if I do get an acoustic.
That hits the nail on the head. Pianists who only play on digital pianos often sound very two dimensional when they play an acoustic piano - I hear it a lot. Generally, the better the piano you play, the more you can get out of other pianos. It's about responsiveness to touch.
Yes, I can see the logic. That said, I guess the cheaper acoustics are unlikely to produce the variety in tone and touch that a better piano can do, so I think to get to this level you do really need to know what you're looking for. So the "wait for a bit and start saving" sounds like the best approach!