How important is a good rack?

That's just like Michael Green, isn't it? I would get rid of that rack altogether, and get something built correctly. Then put a set of Symposium Acoustics Roller Blocks under your table, or better yet, a SA Segue ISO board and then the Roller Blocks between it and the table.

equipment stand or cabinet:)

I found the difference to be night and day. I had now idea how bad my first two racks were until I tried a better one. No turntable here, but the difference had nothing to do with rigidity of the frame. The worse one was more rigid. The better one did not improve with more bracing. Again turntable may be very different.

I bought a fairly tall Salamander Archtype 5 self rack (I don't like bending over to change a record). My turntable is ridged and sits on the top self with a iso platform underneath. This is a awesome entry level audio rack. It does not skip at all when its playing a record ( I could run a jackhammer next to it). There are way more solid and expensive racks but for the money ($250 std blk finish $400 cherry wood finish) it is worth checking out, for excellent isolation of each infinite adjustable self (Mega spikes are a must for the bottom).

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