How important is a good rack?

I have a really nice turntable and some good equipment overall.

I have it sitting in a Michael Green just a rack., It's the entry level with the thinner shelves. I noticed it's not super sturdy if I bump into it it tends to wobble. If I am playing a record it skips. I have an older AR suspension turntable and I can walk all around the rack and it doesn't. I guess what I'm wondering does a rack need to be rigid?

Some rack suggestions would be appreciated. Thanks, Scott
FWIW, the designers of the Continuum turntable (quite expensive?) and it's integral stand said that despite the massive cost, effort and design simulation that went into creating the stand they admitted it was still a poor substitute for a good wall shelf (!)

I must be a pervert - I still use a table ;^)
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.
What you are trying to accomplish is isolating external vibrations from your components. The best rack will accomplish little if it is sitting on a bouncy floor. Wall mounting on a bearing wall usually results in the best isolation.
Best to have 'rackless' room, say hiding the stuff in a closet where the acoustic energy that the speakers produce will not impact the rack and its components. Very important if you have a turntable in your system.
Makes a world of difference - especially with vinyl. I have a Townshend Seismic Stand - they are brilliant.