How important is an audio rack?

No, I am not. Good racks are and should be expensive. I am not prepared to spend $800 or more on it, so as I said, I keep everything including the turntable on the floor. I think, quite a number of people here use Mapleshade racks with good results. Michael Green racks had a good reputation too but no longer made as far as I know.
When I tried Salamander and something else racks, they made such a mess especially at higher volume.

Rhljazz, as far as the isolation/vibration control goes I agree in theory that it could be beneficial. But when I took my gear off my thin sheetmetal rack and placed it on butcher blocks on the floor, I can't tell the difference. I was expecting at least some change, as everything else done so far, improvements were imediately evident. Maybe my components, being so heavy, are'nt as vulnerable and possibly the weight actually tames the rack???

I am not familiar with the products from Box Furniture Company. I do know that Art Dudley from Stereophile has a piece of theirs on loan and seems to like it.

There was an article in Hi Fi+ by Roy Gregory awhile back documenting a demonstation performed at one of the RMAF shows. They set up a demo using the same equipment and speakers, only changing the set-up and substituting the equipment supports and cabling to demonstrate the audible advantages of proper support and cabling.

The quality of the rack will not matter much if some of the other considerations for effective isolation are not taken into consideration prior.

It could be a total waste of money without looking at the big picture from an isolation and vibration perspective first, or a relatively inexpensive solution could turn out to be the cats meow.

Also, the considerations are different for what is needed to isolate a turntable effectively compared to digital gear. If you have both, then two separate sets of considerations to address come into play.

I'm more of a leg man myself =-;)