I love these cars, they are an awesome kit for how much you pay. I have driven quite a few now all different specs (GT man + auto and GTS man and auto) and even the auto isnt that bad the paddle shift rev blip it does is a bit full on at times when you're not racing around (look like a wanker).

Even though the GTS has 'better' brakes then the GT it still fades very quick and the ABS is very trigger happy due to the prius tyres.

All in all great car stock but if i was to get one it would be:

GT manual
Shockworks coilovers
better wheels and tyres
better brake pads maybe even slotted rotors
little exhaust for some note
gut out the intake to cabin noise filter

not sure what else haha turbos would be great but to do it properly would be a full engine rebuild due to very very weak pistons