Hey its Justin with the other A2 GTI from last night good to hear from you.
Here is a list of some things I did.
port & polish the head and shave it call Tom at Total performance for priceshis number is :975-1915 that should give you a hp gain of 15to20.
K&N box air filter about 40.00 easy to do job hp gain 10to20.DONT DRILL HOLES IN YOUR AIR BOX
Headers and full exhaust by Autotech this is really worth it for the money you will have to call Tom at Total performance for the price....it will give you a hp gain of 20to25 (youll notice it)
Neuspeed cam shaft this will help out your top end alot more.

Just take it a little at a time even though its a A2 it will be pricey.
Just call Tom Total performance thats who Brian (red A2 Jetta)and I deal with for after market parts tell him your a friends with us hell take care of you.......Good luck and I hope that helps.