Mate I'll make this easy for you......this isn't me being off with you I'm just saving you the bother of wondering.
You'll squeeze a few more ponies out of the car for a grand or 2.....you wont really notice a huge difference.
There isn't a mod that you can do that will make you think 'wow' from a performance perspective.
You have 2 options......make the car handle, ride and stop better which means you can push harder or you need I believe 8-10k for Proper FI (ie not just bolting a turbo on).
Serious power in this car is hard to achieve without a very committed budget however you can make it handle well and sound amazing for much, much less if you dont mind losing to the scrabble wagons occasionally.