If it isn't broken don't fix it, but if it isn't there add it!
This goes along with a different type of staying stock by keeping the OEM look, but justifying adding things your car lacks but other Boxster's have (like rear speakers, or the OBC).
And when I want to do a mechanical mod, I always remember that Porsche knows more about building cars than I do, and they made the exhaust, engine, etc. the way they did for a reason.