Good idea!
This might sound like complaining but it's meant to be suggestions:
1: change standard cars to premium cars because standards can't get front aero:
As previously suggested, we could change the Volvo S60 to the C30 where you can add front downforce.
I was thinking a little the same to the BMW's, maybe changing to downtuned 135i.
The biggest problem would be the Audi, I don't know what you think but maybe the TT?
2: Maybe allow for a separate race car division with cars like 320i TC, Integra Super Touring Car, Mazda 6 TC, etc..
3: I know you're proud if calling it BTCC, but maybe we should allow touring cars from other Series such as WTCC as well, like the Seat?
Worth to note, just ideas, I way too often get "yelled" at when I come up with ideas