Drive the car for a while and get used to it. Then get a Turbo back exhaust, a fuel pump, a cold air intake and a verso tune. After getting used to your car at stock you will really notice and appreciate the difference. This should cost 3-4k depending on quality of parts.

The next step would a bigger turbo, a bigger intercooler and possibly some injectors. With an tweak to your verso tune to suit you are looking at 3.5k anywhere upto 10k depending on quality again and brand. These mods can have you taking the current HSV range in a straight line...