Please post questions about TXR3 in the "Official TXR3 Thread!"
Anyway, keep your Impreza for now. By an R34 but don't modify it. Wait untill you have enough money to fully mod the R34 (about 300,000CP) then modify it. Don't sell your Impreza after you modify the R34 though as you may need it later in the game for a Wanderer.