Not to be a douche this post is trying to be helpful as im 21 and have 15k in car payments left too. I bought what I could afford, 2008 Mazda B2300 2wd reg cab. I could've bought a V6 4wd extended cab but I could not afford that in the long term and fuel efficiency. My payments are $150 Bi-weekly at 0%, I believe I made an awesome choice. It looks like you should've bought a regular Impreza or just a WRX or turboed your old 4g4d.
How would your insurance company rate the s2k? its considered a two seater convertible sports car. As fast and sporty as the STi is, its a 5 seater 4 door. Also maybe you should not keep spending all your disposable income on upgrades? I know we are all enthusiasts here and that what alot of us live and breathe but what it worth if you can drive the car or afford the payments? In your other thread you have a set of new rims and are looking into purchasing a COBB access port tuner and making an exhaust. I know it says your making one but even if that costs say $20, that's $20 that you can use on half a tank of gas.
You may want to look at selling the car for as much as you can and try to break even and buy an EK civic or something affordable that you can make low payments and have payed off in less than a year and have WAY cheaper insurance. Just some food for thought and my 2 cents.