Here is a thread all about gutting the 00+ airbox.
When I helped Hailey, I didn't cut the whole front off as there was a large diameter hole in it already that was sealed into the fender for fresh air. However inside there was an area that was solid and had a smaller hole in it. I removed a large rectanglar section of this to improve flow across the filter.
There was a noticeable difference...I'm not sure how large though.