One thing I will ad related to the intake is that In my mind, it is advisable to use the stock airbox with the stock ecu, even with the tomsvx intake. I don't know if it has been looked into in our cars, but in maf equipped imprezas removing the stock airbox, or even cutting off the resonator as described in other posts, tended to make the car run EXTREMELY rich at a certain rpm range (around 2K, I believe).
http://forums.nasioc.com/forums/show....php?t=1471819
Now granted they are saying that this mostly affects 05 and uop imprezas, which probably don't even use an ecu like ours, but I suspect a similar situation likely with ours. Unless somebody with an afr gauge and a custom intake cares to prove me wrong.