I've bought this car ~8 months ago, so i'm not yet fully into upgrades -yet- I'm getting to know that car more and more at the moment; I do everything on the car myself, accept the APK (MOT in Holland) 'cause I'm not allowed to do that
But the previous owners did a few mod's; the centre silencer is now a Ragazzon straight pipe, that's the silencer after the katalyser. A TB has only two silencers after the kat, compared to three with every other model GTV. Sound is now a very low rumble at idle, sound gets to normal levels when the turbo spools up (above 2500RPM) but you do get the growl when flooring the thing. Also a nice gurgle when you lift the trottle.
Second mod is an K&N replacement filter and third is an aftermarket blow-off valve (Forge) and last thing not 100% original are the wheels, 225/45 R17 with 20mm spacers at the back.
What I have in the pipeline to do is (very likely) upgrade the (two) ECU; Squadra tuning and that should yield +30bhp/+80nM. According to others that did the upgrade it mostly makes the car a bit better 'drivable' with less of a turbo-lag. Replacing the (original?) shocks with some Billstein ones and for upgrades that's it I think...
So far I've just been busy with fixing the 'regular' things; exhaust manifold leaked (cost me 4 weeks to find it), adjusted the sunroof, replaced door card, improved on the audio, replaced spark plugs+leads and fixed a number of smaller things like knob light-bulbs ect. I'm now looking into a way to read the oil-temperature on the coolant gauge; with a small push button (the one that springs back) so you can see the oil-temp as long as you keep the button pressed.
In Holland there are a lot of TB's around and on the Forum here there is loads to be found. If you want to know anything, just give me message.