I can attest to the AP being an awesome mod for the car. I have ran the car anywhere from stage 1 (directly after the AP came out, and my car was maybe 2 months old). I ran stage 2 for about a year, and have been running a custom map to account for my 20G turbo and supporting mods. I have about 6-7 maps just for my 20G, they go from wastegate pressure up to 20PSI (where we decided to stop) in both 91 and 92OCT so I can pretty much run my car anywhere. If you look around you can find used APs for rather cheap (just be sure that the AP was unmarried from the previous car). Or Cobb has just reduced the price of a brand new down to the price of $595.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX