Ah, the airbox mod, I can't say that it did anything negative to the bike. There is a pretty extensive thread on this with a lot of input from mechanics and technicians that Wavex gathered, but the bottom line is none of them could agree on whether or not it hurt or helped the bike.
For the first 2 weeks I kind of liked the sound, it dropped the engine down about an octave. But then it kind of started bugging me, especially when I would get up over 8,000 rpm, it sounded like it was bogging down, like it had a chest cold, and my air filter was taking a beating. I switched it back before we went on the weekend ride and I'm glad I did, it just sounded healthier.
The new airbox cover cost me $14 American, my advice, by a new airbox cover, do the mod, see what you think, if you don't like it after a couple of weeks, you have the fresh cover right there. Hope this helps.