If your tyres are worn and need replacing, get them replaced and get the wheels properly set up at the same time. I had similar problems with my old GT which was fixed by a £50 realignment.
However, the 147 and GTs are meant to be set up with toe-in (more racing inspired), which generally means more wear to the inner edges of the tyres, so your dealer may well be right. My 3.2 GT wears the front tires on the inner edge a lot more than the other three quarters of the tyres. It's a bit odd because the tyres still look virtually brand new from the outside.
Anyway, get the tyres replaced and get the wheels set up correctly to Alfa's specifications. You'll still see more wear on the inner edge than the rest of the tyre, but it might improve over the last set of tyres..!