I think a miata can do very well in ITA.
There us usually a SM or two that beats the top ITA cars at the races. I dont remember the lap times at the ARRC, but I think they are close.
ITA allows more mods then SM, and now you can run the 15" wheels. So, it would seem they can win.
I have personally thought of this as a possiblity in the future. Love driving these cars...