Well that puts a damper on things. Living in arizona and being tuned at the moment, I'm pretty sure buying an intercooler is a must.Try autocrossing before spending more money as you may want to pick a specific class and that means choices like the intercooler can make for an uncompetitive car because you chose an intercooler that's not legal for a class where the FoST is competitive, so you land in a class that requires a TON of modifications to even begin being competitive at the local level. In my experienced opinion, G Street (only stock intercooler is legal) or Street Touring Hatchback (must retain the grill shutters, AGS, so only legal intercooler is the Vortech) are the only classes where the FoST can be considered competitive.
G Street (GS) is basically a stock vehicle. You can spend money on shocks and a single sway bar and catback exhaust and lighter weight rims (17x8 RPF1 +48 offset are the gold standard).
Street Touring Hatchback (STH) is a nicely prepped vehicle. Spend your money on an LSD, Vortech intercooler retaining AGS, up to 9" wide rims, coilovers, and up to two sway bars. There are some other mods you can do for weight loss & chassis stiffening, but they have minor effects.
Street Modified FWD (SMF), D Street Prepared (DSP), & Xtreme Street A (XA) are the other classes and they allow any intercooler, but the level of modifications required to be competitive are immense. All of them allow flared fenders, very wide tires, LSD, & tunes. SMF & DSP allow any DOT tire, which in practice means expensive Hoosier A7 ($2000 per set). SMF & XA allow gutting the interior behind the front seats and altering suspension geometry and some aero mods. XA may be tempting since it runs on 200 treadwear tires like GS & STH, but the real competitive cars are AWD horsepower monsters (Audi TTRS and Mitsubishi Evolutions).