How much space between cables is enough?

The power cables will create the strongest electromagnetic interference and the speaker cables will be the least affected.     Your interconnects will be creating the least EMI (carrying low voltages and current), and the most sensitive to interference, as all are feeding a gain stage, of some sort.     If you’re an SPL lover; speaker cables might create a little more.     If you can keep a couple inches between, not parallel cables over long runs, and/or cross power cables, at 90 Degrees with anything else: you’re sweat-free.       ".........but don’t get too deep into cable separation." +1        https://www.prosoundtraining.com/2010/03/15/the-emi-project-part-1-introduction/

But doesn't that make the material and design of the elevator somewhat irrelevant? The principle focus is to have the cable suspended by the rubber band.

We don't know that to be the case. Not for sure anyway. When I first tried this many years ago anything that raised cables up off the floor was an improvement. Cable Elevators were by far the best. Cable Elevators are ceramic insulators, designed specifically to prevent electric charges migrating along the surface and since they worked the best it seemed logical to assume it had something to do with insulating from static or electric charges. 

But then I tried a thin coat of Total Contact on them and that was remarkably better. TC is extremely conductive. So there goes the insulation theory. Several very credible people say suspending on fishing line from the ceiling is even better. One of them I asked, what if you use fishing line to suspend them from a sort of trellis? Not as good. Why? Don't know. Tried it, not as good. You have to hang em from the ceiling.

Now I'll do a lot for sound but having to weave around a bunch of wires like Tom Cruise on a Mission Impossible that's where I draw the line. 

But I keep thinking about it. Why? What is different about fishing line hung 8 feet from the ceiling vs fishing line hung a few inches? Well fishing line is sort of elastic. It stretches. But not very much. Its not very springy over a short distance, but over a long one it is. Maybe that's what's going on. Its acting like a spring. 

Well a rubber band is basically a spring. Stretched over the Cable Elevator it suspends the cable like a spring. But its also close enough to still get whatever effect there is from TC. Which believe me, there is. 

So it would seem we have our answer. Its vibration control. Suspending cables in a way that allows their free movement without picking up vibrations from the room is a big improvement. Insulation may have something to do with it but the biggest difference would seem to be due to vibration control.

We're still not sure but a lot of evidence sure seems to be pointing this direction. Still, you never know until you try. 

+1 @rodman99999 

Power cables can run in parallel, closely, and should cross everything at 90 degrees. If you must coil power cables, do it far from everything else, and make the circles as big as possible.

Speaker cables should cross interconnects at 90 degrees.

Interconnects can run in parallel, closely, if they are shielded, like co-ax.

Closely ~ 1".  More than that is diminishing returns, IMO.

@millercarbon

Interesting, I wonder what effect suspending cables from weak springs or 'floating" them on 6" inner tubes would have.

+1 @terry9