If you must spend money, Tuned length extractors, twin 2.25" exhaust system, Cam&valve train upgrade + retuned memcal.
After all that you might have bugger all difference.
I would suggest spending the money on good struts and springs, sway bars and urethane bushes. That will make the car drive allot better. Probably feel allot faster without making more power.
Also the big one, good tyres. You'll get more benifit out of good tyres then you will 1 or 2 kw. And that few kw will cost you a bunch.
Then I'd strongly recomend doing the suspension first. Do it properly.
Not with Ultra low springs and crap shocks.
If you want to go low, invest in some coil overs. Because cars on ultra lows dont go around corners.
Invest in some bigger brakes.
Give the buick a dulux rebuild and keep it looking clean untill you can get a better motor.
The more money you save now, the better your first car off your P's will be .
I agree with soop on this 100%. Suspension was the first thing I done on my first car, just some low (not super or ultra) springs and good shocks. Makes the car 100x better, ive got complements off people about how it sticks to the road around corrner's coming from VE drivers trying to folowing me in there car.