I have had cables raised off the floor and have yet to hear a difference. Now it could be that I have only ever had a listening room in the basement where the flooring under the carpet is concrete and in my specific case there is no issues.
My preference would be to go with ceramic or porcelain that look like this:
Brownelevator.jpg
They have some weight to them and are easy to work with.
Even if they do not add to the sound it can help with cable management. Also they look cool.