Yes 3D prints can be sanded pretty well, PLA at least any way, ABS is a touch more difficult. The ash tray holder in my MK1 Escort had all of its corners chipped off. You can get re-productions for about £30 on Ebay, which seemed a little steep to me, and I hate the little metal clip that holds it into place. I designed and printed a new unit that kind of self clamps itself to the centre console without added hardware. Sanded it and spray painted it satin black and honestly you wouldn't know the difference. I haven't got any pictures on the PC however. I have also printed some custom GT style centre caps, which I do have pictures of. I didn't do them to as high of a standard because they are on the wheel and will be getting hit by chippings and debris from the road, but are still pretty effective.
On this note, if anyone can think of any hard to find parts, like the air vent above, that would benefit from being reproduced, I'm always keen to take on a new challenge!