Just to comment on one point. Spectator experience - as illustrated in this vid from the recent D1NZ at Pukekohe, the cars disappear behind the fences after the front straight, there is only the tyre smoke to indicate the positions of the cars.
https://youtu.be/cxMkTO7vLpw?t=4m17s
Would touring cars require coloured aerials (etc) to indicate their positions to the spectators.