since suggestions are open i'll throw in a few....
add a class for cars with mow-medium power and low weight which are rather focused at acceleration like the Lotus Elise or caterham, or maybe with power restrictions cars like the Golf GTI RM which is slightly tuned so its light and doesnt have much power.
also i'd say make themes
for example have a classic japanese tournament in where you race on fuji or suzuka in a datsun Skyline 2000GT-R and stuff like that and the AE-86.
or a race on laguna Seca with mustangs corvettes and Vipers.
also a possibility is we do a classic vs. modern race like lets say the Dodge Challenger R/T (slightly tuned) vs. Dodge Challenger SRT8 '08 stock.
another match is the Ferrari F40 slightly tuned if necessary vs. Stock Ferrari Enzo (nicknamed Ferrari F60).
or go head to head with born rivals like the BMW M3 E92 vs. Mercedes C63 AMG
or the Impreza WRX STI vs. Lancer EVO
or a Ferrari F430 vs. Lamborghini Gallardo LP560-4
also we can do a last man standing style tournament.
before the race starts we plan the race here on TDUCentral and then we race head to head in short 2 laps races till the last man stands. and the rest of the party can watch the race and be the judges in case one of the racers cuts a corner or something.
and maybe if there will be a winner in each class have them take it on haed to head for a prize lets say a color chip or tuning parts, or maybe even a car......
these are just some ideas that i had in my head.....