I've owned 2 different 2002 WRX's...between them, I've spent a fair amount of time at various stages of tune: Stock, stage 1 (ECU tune), stage 2 (ECU tune+tback), VF34 turbo swap, and finally, a hybrid build (2.5 from later year, 2.0 heads, 18G turbo, TurboXS IC, injectors, pump, dyno tune, blah blah blah...)
I haven't taken it to a track; the car's 11 model years old, and I need to keep my transmission in one piece. I suppose you could make a case that my current car is no faster now than when I started with it 7 years ago. Being an engineer, I suppose I put more credibility on empirical measurement than that. The Mustang dyno where my car was tuned suggests that it's putting out around double the torque of a stock 2002 WRX. The car generally pulls like a freight train, and I had to let up a few months ago so I wouldn't bump into the back of a new generation STI that was trying to pull away from me.
Good enough for me.