It depends...In my case I'm working with an SL1200 with stock feet. It sits in a composite rack which sits on carpet. Therefore it is not directly coupled to the floor which is 2x4 with plywood underlayment. The rack does NOT sit between the speakers but is on the other side of the room, 20' away. I don't believe for a moment that putting wheels on my rack will make any noticeable negative impact on the sound quality.
It all depends on your room setup, what you put the turntable on, it's footers & suspension, etc...