You'll have to spend plenty of money just to get to STi performance and once there, reliability goes out the window. (I know this first hand with my wagon). I would start with a better drivetrain platform with a jdm longblock (2.0L w/forged internals) and tranny or with the usdm version (2.5L). Or, sell your current wagon and get an '06 wagon and join the 2.5L crowd with a brand new car.