How important is an audio rack?

If your gear is that prone to resonance and vibrations maybe your using the wrong gear.
Gshepardbuster

Actually, it's the other way around. The higher the resolution of the component, the more likely you are to hear a difference. Not so much a problem for mass market and mid fi components.

Very few products at any price attempt to address internally generated harmonics or reduce externally transmitted vibration. Some CD players have sprung transports for example. There are amplifiers with floating circuit boards and Berning even uses Stillpoint devices in some of their amps to isolate the boards. Some of the casework on my VAC preamp is damped but it still is not immune to the stand or the room. All transformers create noise.

I generally find I like Stillpoints and spikes (although I don't buy into the vibration draining theory, whereby every resonance in the component is grounded through the spike)

Racks are expensive to try out, but maybe trying some of the footer tweaks would prove enlightening.

Rhljazz/Inna
The rack the salesman was raving about was from Box Furniture Co. I'm curious if your familiar with this 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.