Un-say "intake"....aftermarket intakes do virtually jack for 09+ wrx's (or earlier 2.5's for that matter). A good friend of mine is pushing over 450whp on his...fully built, custom turbo, etc....and stock intake, because he tried out a few and didn't gain anything more than noise from them. The general opinon on the Subie forums is that intakes are more or less a waste of money for performance, and only good for "bling" under the hood.
You can get an SPT exhaust if he doesn't want it too loud, and it's borderline legal too, since they came as port-installed options on "SPT Edition" cars like mine. I get tons of complements, and it's loud enough to be noticed, but quiet enough not to be annoying. The "word" is that it's good for about 5whp on a stock-tuned car, and it's fine with the stock tune.
Accessport is nice, though you can go opensource for alot less money. I have an AP I picked up cheap and I"m just running a stage 1 tune (stock everything except the SPT exhaust). It really smooths out the midrange and gets rid of the mid-high detonation due to lean running that the stock tune has.
My 09 untuned with the catback put down 251whp and 252wtq (only about 2% lower than the stock 08 STi that dyno'd right before me, I might add). With the AP Stage 1 tune and no other changes, an hour later it put down 253whp but 282wtq. Much nicer "area under the curve" and hugely improved driveability.
Stock tune A/F is TERRIBLE....running 14.5:1 up to 3500rpms and full boost, then plummeting to 11.5:1 by 4500rpms as the ECU pulls timing. Stock tune is LEEEEEEAAAAAN for the sake of emissions. And trust me, you can feel the hesitation like a mofo when it pulls timing under load at 35k....
Post AP Stage 1, A/F is 12:1 at 3000 and slowly tapers to 11:1 by redline. So much nicer. And so much better for the engine to not be detonating under WOT all the time.