Just a brief note to point out rigidity per se is not necessarily a desirable characteristic for support structures inasmuch as structureborne vibrations can be more easily transmitted through rigid structures than if the structures were wobbly or flexible, which was the idea behind the Flexy Rack of yore. Isolation from vibration can be defined as the ability of the support structure to move easily in the direction(s) of interest, say the vertical direction and all horizontal directions. That’s also why you can push the top plate of a good isolation stand and it moves very easily at the slightest touch. You could say it's the opposite of rigid.
System platforms
I recently bought a new rack for my system. It's not an audio rack, I couldn't afford what I would've wanted. I wound up getting what is essentially a workbench. I liked the industrial look and it went well with the tubes and the industrial look of the components. I wasn't expecting the large improvement in the sound. When I did it, it was an aesthetic improvement not an audio improvement, or so I thought. I have the cables, the power cords, a Richard Gray 1200s. Currently I have a decent system, moderate to low end on here but before the divorce I had the crazy system. The ML 33h, Lexicon MC12B, etc. But this was night and day. The audio quality was greater than any cable change I've ever made. If you are on the fence about getting a better rack for your system I hope this gives you a push.