I think there's a difference between performance modifying and rice modifying.
My car has a completely stock body, with only oem parts - however, I have changed the exhaust, intake, decat and chipped it, purely for performance, yes it has a 110mm exhaust tip at the end of 70mm piping - but thats for performance?
Granted, without the silencers (which I do take out on occasion), its loud, and you can hear me for miles, but again, taking them out increases performances...
I don't pull up next to citi-golf's and rev my engine - I've done this purely for me... and for performance gains. Why should I buy a faster car at four/five times the price when I can modify mine for a third of what it cost to meet the performance of other these cars?
The manufacturers make a good vehicle - that doesn't mean a 3rd party can't improve that design - does it?