If you can get a tune for that money, do that. Factory the ECU does run rich and you can make money + more economy with a simple tune. Plus the car will feel a lot nicer to drive.
I have a version 8 WRX wagon and all I have done is:
- TD05
- Silicone intake
- Deatchwerks DW200 fuel pump
- Spark plugs
- Decatted downpipe
And a road tune and the car feels 100x happier and wants to move.
Be careful what you read on the Subaru Parts NZ page.. there's more to it than bolting on a VF30.
Realistically, what I would have done in your shoes is saved up, bought a 2.5" Turbo back exhaust, DW200 or Walbro fuel pump, turbo of your choice then get it all installed and straight off to get tuned. Then look at an engine later if your current one is limiting power or blows up.
And also read: http://clubsub.org.nz/forum/showthread.php?37777-How-to-get-power-out-of-your-WRX-STI