Unless you want to go down big power figures and change your turbo, there isn't much else you can safely get out of these cars.
A front mount intercooler, down pipe, full system exhaust and maybe an air filter to grab a few extra bhp but nothing that will be ear pinning back speed!
I would personally pay attention to the handling and braking - uprated roll bars, anti lift kit, lowering, uprated bushes, big brake kit.
What year is your car? Maybe some styling mods?