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

I wouldn’t worry about it in most cases.

However isolating signal wires from power cord runs and power cords from each other is usually a good idea no matter how that is achieved.

Gosh, you don’t say, moopman?

I don't start a CD until I've paused the track rather than stopping it and then pressing play.  Tom Port of Better Records demonstrated the difference about 14 years ago  After I began using my Walker Talisman about 13 years ago, the difference was diminished, usually I can't tell the difference between stop/play and pause play once I do the pause/play from the first track on the disc.

So here it is, Raising cables Works !
Large sound room,big system..lets tweek. Carefully suspended my cables from the ceiling using knob & tube technolog, as per the likes of John D.Harnden Jr. General Electric Engineer (Retired) and others. Strategically hung (clothes line style) cloth tapestries...Bingo Audio tweaking bliss ! Bored with the hunt scenes etc. down came the tapestries. Renovations gifted me a temporary cache of my girlfriends high end lingerie...Another Bingo, Visual & Audio stimulation !!
I'm minus a girl girlfriend & most of my female friends.
Further research left me tapestries on walls,wool area carpet,leather furniture,comfort and detailed audio sound. 
And finally my appropriate length wires / cables are separated as much as possible and on the floor !!
Research and knowledgable friends will save you money and aggravation dealing with scientifically baseless stupidity.
If given the opportunity look around at the wiring in a recording studio ...that'll make you smile.
Cheers

Makes zero difference.