Have you thoguth about the usual ecu chip/remap, exhaust upgrade, filter upgrade.
They are the usaul things to do first and will release a few ponies.
If you do go for the cams and st170 manifold above i would highly recommend you let the car breath by the menas of filter and exhaust to get the most out of it all.
The world of tuning is vast, its a question of how deep ur money pocket is!!!
Macca