1. Why do some folks with usually higher end systems use those cable lifters to keep the cable elevated?
No idea why some folks use them. I use them because they greatly improve sound quality.
What are they intended to do?
Greatly improve sound quality. I've done demo's. Its easy to hear.
If you use them what do they do for you please?
Improve clarity, detail, soundstage depth, and focus.
And if you know do they make sense from a purely technical standpoint?
Probably. But it took a while. They would seem to make sense from a dielectric point of view. Everyone knows the importance of quality insulators in cable design. Then you go and lay your cables on carpet, or wood, or whatever that is nowhere near as good as teflon or other quality dielectric. Cable Elevators are actually ceramic insulators, designed to insulate and prevent the propagation of electric charges.
So for a long time this seemed the most likely technical explanation. Until I coated mine with TC, which is highly conductive, and they work even better. So it can't be that.
Cables vibrate a great deal. Hold one some time while playing music, you will feel it. What if the real reason is they hold up off floor vibrations while allowing the cable to move freely? This I think is the correct answer. Because the effect is greatly improved by using rubber bands to suspend the cables above the cable elevators. https://systems.audiogon.com/systems/8367#&gid=1&pid=10
All my cables- power cords, interconnects- are suspended on cable elevators with rubber bands. I don't do these things for no reason. You never in your life heard a system this good.
2. I bought a bunch of those gold plated caps to cover all the unused RCA jacks on the back of my AVR. I believe they are intended to keep noise down. If you use these, please comment on them. Do you think they do what they're supposed to do, and/or do they make sense from a purely technical standpoint?
What is this obsession with technical explanations? If you hear it, will you not use it unless you can explain it technically? What if there's a great technical explanation, but you can't hear it doing anything? Will you buy it anyway?
Let me save you a whole lot of time and trouble. The vast majority of technical explanations are either wrong when used, or will be shown years later to have been wrong. The very few really good technologies (Tekton, DBA, etc) hardly anyone understands anyway. They're good, but nobody gets it. Even though DBA has been around decades still hardly anyone gets it.
So enough with the technical obsession already.