I'm sure that a solid stand with no resonance would have some effect on the sound but in my situation convenience trumps that consideration. I've got an all-metal rack from IKEA that I like better than anything else I've had for one reason, it has wheels.
Because I'm constantly adding or swapping pieces as I play around with things the ability to roll it out and turn it to the side to get to the cables and the backs of the components is great. I'd guess it has saved some wear and tear on the gear, too, since I don't as often have to move them in and out of the rack.
I made some concession to the usual concern about the metal rack 'ringing' by covering the bottoms of the shelves with sound-absorbing sheeting. I also put the components on sorbothane pucks and then heavy tiles. The convenience factor easily outweighs any other considerations for me.
Because I'm constantly adding or swapping pieces as I play around with things the ability to roll it out and turn it to the side to get to the cables and the backs of the components is great. I'd guess it has saved some wear and tear on the gear, too, since I don't as often have to move them in and out of the rack.
I made some concession to the usual concern about the metal rack 'ringing' by covering the bottoms of the shelves with sound-absorbing sheeting. I also put the components on sorbothane pucks and then heavy tiles. The convenience factor easily outweighs any other considerations for me.