I had the upgrade on my GTA, I don't believe it was necessary to have the 330mm setup, I don't believe that the brakes were underspecced for the car, mine warped at speeds under 50mph I reckon a defective batch of calipers is more likley as not everyone was effected but hey I wasn't about to complain
my discs warped approx every 3k and I had 4 sets of discs before getting the upgrade, my dealer was cool, basically told me that before I can get the upgrade I have to go through the process of disc chnages etc. for suitable justification, after so many sets I got the upgrade FOC the only real hassle was that the brake pipe was out of stock so they had all the bits for the change but the pipe but hey not every manufacturer will sort you out in this manner so I was happy to wait, as for it being a recall, its not that serious, you will not really loose any breaking efficiency, its an annoyance thats all.
My dealer was Victoria Park Alfa in Cardiff, after the upgrade the brakes felt good but then they always did even with the 305mm even warped, I have had that same 305mm setup on other cars with no issues and they were a lot faster, no warping issues even with track use, so reckon either bad batch of discs or calipers but as Alfa were speccing larger on newer models it was just as easy to solve that way, the reason for the increase most likely being because the number of magazines that commented on the Alfa having smaller setup than its direct competitors (Ford/VW etc.) despite the car out braking all of them.