You mention comb filtering. Indeed that is real and measurable, but as has been stated by our gracious hosts here, it is not actually all that detrimental.
I have a semi-secret audio production technique that I use for widening sounds. It purposely introduces comb filtering.
Here's a quick wave file, the first snippet is in mono, and the second is the same mono source passed through through the comb filter effect I built.
See what real world effect it has...
http://www.clubneon.com/test/Neon-Comb.wav
