Poor throttle response is mostly due to your transmissionm which I'm assuming is automatic. A flash tuner will help with that and improve your shifts, and add some horsepower and torque. An SCT Xcal 2 is $400 and well worth it.
www.vmptuning.com. The J-mod shift kit is another good mod for the auto tranny to firm up shifts, found at
www.vapauto.com
That spiralmax thing is a bunch of BS. Expect to be spending about 50$ per 1 horse power for most mods. lol
The cheaper mods for good power and performance are 25% under-drive pulleys, which will add around 5rwhp 7rwtq, cost around $200-230.
Getting new rear end gears and t-lock (posi-traction) will help your acceleration a lot, and will make both of your wheels spin. 4.10 gears and a T-lok is around 600$-100$ including install costs, depending on your luck.