I can't speak for the relative popularity of those classes at your track, but at my track, stadium truck has gotten a lot smaller with the advent of Slash spec class.

You might want to look into the Slash, because 1. it's a hoot to race, 2. the trucks are cheap, and 3. the slash is darn near bulletproof. Spur gears and shock caps are the only things I've seen break at my track, even in our premier event which had about 50 entries in the Slash class.

That said, buggy is usually pretty popular most place, as it is here, but you've already got a T4. Why not pick up a new B4 or T4 and use your old T4 for backup parts?