Only a couple of things I'd really like to see something done with as think overall there isn't too much wrong with the league
F1s - like marten suggests, either more damage or stickier fences (thinking Bradford style). This might produce better racing and stop some of the OTT stuff as if you stick someone in the fence they will stay there but you then run the risk of getting payback in the same way. Currently this isn't an issue at most tracks as you can get away with bouncing off the fence or wall riding thus not having to worry about any consequence (losing a fair but of time/losing a points place) of any payback.
It could also make lower graders think twice about firing blues/reds/ss in after getting passed cleanly as they will know next time they wont get passed cleanly but end up in the fence themselves thus having a proper consequence to their actions, just like in real life. Obviously this would also apply to anyone getting passed cleanly by a faster car.
NZs - cut down on the team racing in the normal meetings by allowing no blocking or waiting for other cars until half race distance, this would mean people would have to try race from the off. Don't think it should be banned altogether as having read FWJs new book he says a lot of the NZ lads went out to stop him winning and the English lads would help him so it does happen in real life