Step #1 Finish our cars. (I'll need someone to float me about $35k)
I would toss out times in scoring the event and just assign points based upon order of finish in each discipline. That way if someone blows everyone away in the drag race he dosen't get a point's cushion to protect him in the road course, slalom, braking etc. It would prevent someone from building a one trick pony and require balanced performance. After all, that is the idea behind these cars is it not? Concievably someone could win the whole enchilada without winning an individual event if their car is consistantly among the top few finishers. I think that would speak to overall build quality (reliability) as well as the design and implementation of various systems.
1st - 5pts
2nd - 4pts
3rd - 3pts
4th - 2pts
5th - 1pts
Of course you could stretch the placing and points out if there are more participants.