There’s a running joke that it’s always a Scoob that’s the first to break down on any given track event...
I had a blobeye DCCD STi PPP for a few years, and took that to track days both here and abroad. I also tracked my old 350 a few times too. I used to run a mk1 MX5 as a track slag, and I’ve just done my first track day in my mk3 MX5.
I get what you’re saying about the Scoob, but the easy tunability and availability of parts is incredibly tempting. You don’t say here what you’ve actually got, but there must be more to do to it to get more out of it. To get a 350 to competitive levels in TA will take a fair bit of wedge, and I’m not convinced any cheaper or more reliable at that point than doing it to a Scoob. Now an MX5 on the other hand, immense fun and cheap as chips, but TA winnable? I doubt it. @docwra has it spot on when he mentions Elises as the way to go.
If it’s cheap fun you want, then hell yes a boosted MX5 will have it in spades and be comfortably better handling than either of the other too. Competitive maybe not, but you could end up with something as quick for a smaller budget, and that chassis is immense regardless of year.
I don’t have any direct experience of TA, so make of that what you will in my comments. Having tracked all three cars you mention, for fun I’d be taking a stock NA MX5 over the other two for pure driving thrills any day, plus less concern to your wallet if you bin it. A boosted one would be nigh on heaven.
I really want a set of ITBs for mine