This is just my observation of the fans; the casual fan is just there to watch the nitro cars anyway, and to get as close to those guys as possible when they are not on the track. They dont care about Pro Stock, Pro Mod, or the bikes so why would they want to watch any "slow" sportsman classes regardless of the format when they have just seen: cars going 300 mph, header flames 4 ft in the air, stuff blowing up left and right, and having it feel like an earthquake every pair of cars. Then they can follow them back to the pits and be 10 feet away while they service the car...
I realize not everyone is like this and there are people who go to watch the sportsman cars, I am one of them when I am not racing.
I think the "90" classes are fine the way they are and don't need "fixed". I am pretty sure that every D3 race I have been at for the last 3 years has had the largest car count in either S/C or S/G... Could be a different story in other areas? I think a more balanced entry fee vs payout would be great especially when you can routinely go to a local track, pay 1/3 the entry fee, win $1000-$1200, and not have to be there for 3 days.
Ok, I'll shut up now... just offering my $.02