Does raising speaker cables off the floor really make a big difference?

It's a relatively cheap tweak to try out for yourself. Just get a Jenga set at a garage sale or cut a 1x2 furring strip into 2" lengths.

you dont know high end sound without cable risers.

mwhahaha

The best cable riser demonstration was at a show several years ago, perhaps RMAF. As I entered the room the demonstrator was using a foam-ish cable riser, I believe of Shunyata make, and rubbing it against the top of a CD. It was being used as an anti-static device. It worked to some degree, better than as a cable riser. 

Want to test this essentially for free?
Cardboard egg cartons. Cardboard is a great insulator for this application.
Cut each carton (discard the lid) into 4 equal sections. That gives you 3 egg holders per section.
Note the shape of your pieces, they even have ready made seating notches for your cables!

You could hose down the carpet with an industrial strength anti-static spray. If static is all you’re worried about.