How important is a good rack?

Good is always better than bad.

A good installation means components including speakers sit on a solid foundation that is resistant to vibrations and movement. So whatever the stuff is resting on should provide that. Can be a bench, shelf, rack, whatever one prefers. Does not have to be pretty or fancy. Those are aesthetics which is important but has nothing to do with performance.

Also teh floor that things rest on is part of the foundation and often the only foundation in place in the case of floor standing speakers. One has little control over this but should be aware that the floor is a big determining factor nonetheless. With most modern consruction houses, lower floors will tend to provide a more solid foundation. First floor directly on houses foundation concrete slab is the best. So take that all for what its worth in each case.

ALso keep in mind that the higher off the floor components are located, the more susceptable to movement and vibrations they are so that ups the ante for teh build quality of the "furniture" needed.

I put my best gear on a low standing solid wood bench on teh lowest level of the house. The concrete foundation and low profile of teh solidly constructed wood bench provides a most solid foundation for everything and the sound quality reflects that accordingly.

So the general rule is to keep everything as close to the ground as possible in order to provide the best foundation. Ther further away from taht you are, the harder it may be to achieve similar results.

Matters most for mechanical devices like turntables and speakers and disc players to a lesser extent. Much less so for amplification equipment

You knew the Kate Upton comments were coming. Obviously hers is quite important to her and advertisers. It makes her a superhero in video games and such as well it seems. 🌝

"So Mapman what your saying is if your turntable is on the top shelf the closer it is to the ground helps with vibration?"

Yes. Lower for turntable is easiest to provide the desired solid foundation. The higher up the harder it is.

The thing is with a vertical rack the turntable usually goes on top for easy access. That's the worst place though in terms of managing vibrations that can affect performance.

If you can put the table on a low solid platform, bench table, whatever separate from teh rest, that is a cheap easy and effective solution, if you have room for it.

I'm not into wall shelves myself but some swear by them.

I suppose the wall would make for a better foundation than many floors, especially in modern houses with suspended plywood flooring that has a lot of give. Nice during an earthquake, but not so much when the tonearm starts flying if you start to boogie down.

If one has the option of acoustically isolating turntable from speakers, then that is worth it for sure.