My stuff sits on wooden shelves, but an extreme audiophile I visited had sturdy metal racks; the kind you see in Stereophile. Since his sound was the best I've heard, I know they make a difference. I believe the question "How much"? is related to the depth of one's pockets.
How important is an audio rack?
The difference in opinions is almost as heated as the great cable debate. Many claim solid hardwood is best. Others like no shelves but some even defend mdf shelves. One store owner/salesman stated the audio rack should be considered the most important component, even with a very modest system! My opinion is much more moderate, but i'm curious what others think.