i believe this is a matter of personal prefference
to me it's like this:
1 pick a nice car when u buy one (celica is a great choice... plain stock it looks good

)
2 the car definitely needs a good music install!!!!(for this one i work my ass off!)
3 spend some money on original looks
4 spend some money on performance
currently i'm halfway stage 2 and i'm getting into stage 3
i have a nice audio install, although i still need a good compo and want another powerfull tantrum amp
currently i'm working on a nice buildup of my trunk so that's the audio stuff mixed with the looks of the interior
when all this is done i'll start saving money for a veilside kit body kit
don't know yet if it 'll be the complete one or just the nose... i kinda like the ass of my celi already
and i have some "original" ideas(=> haven't seen it done to a celica) to even make it better
after that (by this time i'll be a working and making tons of money so money won't be an issue (plz plz plz pzl pzl pzl

)
an engine swap might be up
engine swapping is something i'm reading up on for the moment... it seems to cost a lot... but i'd make my st a LOT more performant...
i'm still studying... maybe i'll have to money when i graduate and start working... we'll c
oh yeah and i also like those custom leather interiors so ... if i have some money in the future it might consider this...