all the problems you had with the 159 will present themselves with the GT - and probably more besides! e.g. inlet manifold problems (unless the car already has the uprated manifold fitted or is pre 2006), egr problems, turbo solenoid issues, clutch issues, turbo issues, MAP sensor issues, oil cooler pipes & rad, rattling tailgate, door check strap issues, cambelt and waterpump issues etc etc.
If youre looking to go back to Alfa ownership because you miss an alfa and the maintenance problems didnt put you off the 159, then go for it.
If youre looking to go back to an alfa to get the looks, please the missus and not have to worry about maintenance and the associated costs, probably not the best move!