I agree with Mike, valves don't just warp they burn. The pic you posted looks like a layer of carbon build up which could be removed by sandblasting. You would really have to show us a close up pic of where you think it is warped from. I have seen many ugly looking valves from DSM heads which my machinist is easily able to clean up and after a 3 angle valve job, as good as new.

Either way, tune has nothing to really do with that, that didn't happen in a matter of days or months. You ever see a stock DSM AFR map all in the 9.x range? 14b's running 12-14 psi pumping out 160WHP on stock DSM's. Running that rich is not gonna kill anything at all, it will not damage any valves or your motor, and Mitsu engineers knew that back in the 90's