How much difference does an anti-vibration audio rack make

bsmg. I use shelves with glass racks and use butyl rubber size 10 bottle stoppers. rather a bit like you submarine plugs... I must own a hundred of them.            
The one negative of magnetic support is the floating object's vibration has no where to go. So the airborne vibrations hitting the box. just keep it buzzing. So the floating boxes would need to each have a way to internally dampen out those vibrations.

Yes, Elizabeth, you are correct. I failed to mention that the encased magnets should be in some sort of oil solution so that they have no chance of banging around inside the support column. I’m sure there’s other bugs to work out in something like this.....I just think it’s an intriguing idea. Pro Ject makes a turntable with this type of support; the Perspex.

They make a big difference with turntables. Otherwise, not so much.

I built a magnetic levitation stand twenty five years ago. It’s the same idea used in the Verdier turntable to “float” the heavy platter. And similar to the air bearing platters and air bearing tonearms. The general issue with mag lev is that the sideways forces of the opposing magnets are very strong, such that the top plate always ends up pushed against the part of the structure, e.g., the column, that stops the top plate from flying off the stand.
This also prevents the top plate from moving freely in the horizontal plane, I.e., no isolation in the horizontal plane. Also, not good for isolation in the twist rotational direction.

So the top plate is not totally able to float and a transmission path is formed between the bottom part of the stand and the top plate allowing vibration to travel up to the top plate. The magnets themselves do not make contact if you do it right. A better solution to the problem overall is a combination of springs and roller bearing assemblies, as has been discussed many times, which can provide isolation in most or all of the six directions of interest, if you do it right.

They make a big difference with turntables. Otherwise, not so much.

Incorrect. Well designed racks and isolation devices provide a significant improvement with all audio components - in addition to TT’s.