Honestly, there aren't really any "performance" gains for straight line performance to be had without major work when it comes to 2.0 NA.
Custom extractors, no cat and cat back exhuast would see a gain, but probably at well over $1,000+
Cat back exhaust will add to the driving pleasure (re: noise) but performance gain would be minimal.
Intake is 100% placebo effect, no real performance gain.
So in short, save your $$. Upgrade intake/exhaust for asthetics only if you wish, otherwise save up to trade up to a GT
However, handling performance can definately be improved = quicker round the bends. Spring/Shock combo (Tein's on Bilsteins etc) and whiteline sway bars front and rear will see a vast improvement if Hills runs is your thing. If "cutting Laps" and drag races is your thing, sorry not looking bright.