I've had a 1.6 Petrol 147 and i now have the 1.9 JTD GT.
Check the rear wiper hasn't seized, and all the electrics work ok (cruse control etc).
Alfa's don't have a problem of rust anymore like the old ones.
As for the JTD, I've only had it a few months, and my EGR has needed replacing (or you can clean it) already, you need to get a decent battery (for the cold weather), there are problems withn having a DPF (if the 147 has one, I've been told the GT doesn't) and you sometimes get a 'water in the fuel filter' error message and the fuel filter doesn't have an accessable tap to bleed it, without taking it out.
All in all, have it checked out properly and take care of it, and you shouldn't get any problems (i had my petrol 147 for 2 years, and it never broke down or didn't start).