I had to make a lot of improvements to my WRX, almost everything. The idea was to make a "real" rally car, so the upgrade was with turbo Lv. 2, Suspension, trasmittion, weight reduction, etc. With this upgrades, I could beat all the cars, except by the Ice Arena races, 'cause it's too small and couldn't find a place to overtake. Had to make wall ride in this one. But I could even beat the S4. They were always behind for a sec. to 8, it was all about the track (always close on Tahiti, always a "landslide" on the Alps)
What I'm saying is that is a big deal to buy the Impreza WRX (the newer, don't remember the complete name, 2003 model I guess...) and then upgrade it. I spent around 150.000 Cr or less. While a rally cars costs, how much, 500.000Cr?
Don't know how do the other Imprezas work, but this one is really great.