i think it depends on what you are looking to do with the car. with limited cash, i think it's either put it all to getting faster, or all for looks. so it depends on what you're looking to do, or which you'd prefer.

if you decide on rims, you have to decide between looks (17s) or function (15s).

are you keeping the car for a while? if the chassis is in good shape, you could always turbo or sc the car, and replace the engine when it goes (assuming the rest is in good shape).

just make wise well thought out decisions...nothing like making a bad choice with the limited money you got (i know i've been there).