I agree on the GS trim GTI vs STH. Opening up the rules leaves more knobs to turn, but that comes at the cost of having to learn what works / doesn't. Street class was great in the fact that it limited everything. I loved the GTI in stock trim and never even went super in depth with alignments or anything (which in hindsight would've made it even more fun/competitive).
I've been trying to challenge the "full build" aspect of the class rules since I started in STH. Doing mods in steps has helped me understand what makes the biggest impact while keeping budget in check. Some people have budget to go from zero to full build in a single season, and I guess I'm sort of taking the time to learn for myself (and with this chassis in particular) what is really necessary for autox. I think I'll end up with what I would consider a full build well before I run out of rules to bump up against + parts to bolt on.
From previous Subaru STX and STU builds, I've learned that you can get 95% of the way to competitive in ST with wheels/tires, sways, neg camber, DP, tune, alignment, without going full build.