Hmm, the best list I can think of which actaully be quite affordable.
1- STi front splitter for the bumper
2- Debadged carbon fibre grill
3- STi large spoiler
4- Set of 17" versions of the wheels you have now (STi wheels)
5- Tien Coilover suspension kit
6 Set of Morette headlights. They break up the strange circle lights that Subaru decided looked good
But along those lines wont cost the earth and should make it look soemthing like so... (ignore the stickers but thsi is the effect).