I had mine remapped a while back by Austec Racing at Crawley. One reason for using them being that their rolling road can take 4wd vehicles. Austec's mainline is TVRs and similar but have done a number of Alfas.
Out and out performance is a little better, but the most noticeable improvement was to the the car's general response and flexibility (vague terms I know, but hopefully descriptive). The other thing they did was to reset the rev limiter which if I recall correctly is set rather low for first gear, owing to the low gear ratio chosen by the factory. Limit now is 7500, but rarely explored!
Downside is that fuel economy has suffered, but then I didn't ask for that to be the over-riding parameter!
Shortly after the remap, I fitted a K&N replacement filter which made another small step improvement in performance. If I was doing it all again I'd go for the filter first (about £45 + fitting)
Cost of the remapping - and this was just over a year ago - was about £280. Rolling road would be extra of course.
Guess you'll want to think about brakes next.........
Hope this helps.