I think the Spec C and RA would both be great cars, but realistically are you going to do any track work or anything where you'd see the benefit?
Also the investment thing.. you know how I feel about that. I appreciate that you don't want to lose a shed load of money right away, but they're all however old now, they're not going to lose much, regardless of the model.
The JDM Hawkeye STi is still a very very good car. Usual exhaust, intake & remap will see you over 350bhp in a very responsive and well handling package. They'll support a twinscroll turbo beyond 400bhp easily too.
"Choice mods" - everything can be reverted to standard for sale, except if you go full blown nutter.
Have you had a drive of any of them yet?