The reason I bought mine was because it was stock (engine wise). There are so many modded WRX's here in NZ. They all have the same, more often than not, badly done mods. Pod filter, BOV & cheap exhaust that's all sound and no gains.
The only things that it had done was lower springs, front lip and wheels.
Since I bought it I have replaced the wheels, so I can fit 235's. Didn't go to 18's though, stayed with the 17's and put 45 profile tyres on. I think it's a good compromise with the stiff suspension and rough roads here in NZ.
No doubt I'll slowly add bits and pieces to it, as I now own a house with a large garage / workshop. :-)