Do you actively compete with the car? Or do you just do it for fun?
My approach is to build a car the way I like and to hell with the rules. If I end up in some tube frame 600hp class because I have a triangulated strut tower bar so be it because all I want to do is have some fun and improve my skill. If I wanted to be competitive in any form of motorsport I'd purpose build a car for it. But then again I've only done one event so my opinion doesn't count for much.