I think there are much bigger differences between example of what started as identical cars than between the models. In the big wide world a 1600 and 1300 are much more like each other than anything else. The 1600 has the bragging rights: its rare, expensive when new and expensive now. Harder to find, harder to restore. Pulling out the pub car park and off down the road the differences are marginal. Some of the 1600s also bring compromises with suspension and seats. Maybe they'll pull an extra 0.2g on a test track and as homologation specials had all sorts of little detail changes the works team were gagging for, but as a road car?
There are some very fast 1300cc race spec Fulvias, if you want to race, but I went "one cam change too hot" with my Aurelia and it became harder work in London. Even on A roads it was grumpy in 4th gear unless really cracking on, which is a rare thing to be able to do.
Can change springs and dampers and camber, and shave a second or so off your lap time, but make it really heavy to park and destroy the ride such that it becomes a selfish pleasure not a car other people want to ride in.
It depends "on the use case". Is this something you'll use "like a car" or is it replacing a motorbike? Do you want to cover a lot of miles on normal roads or roll it off the trailer at events and try and win something?
There's a "my fulvia is uncomfortable" thread. Its not a race spec car but might have some pattern part springs the wrong rate, it might be the interleaving has failed, it might be bushes, it might be old tyres. A journalist might hop in that car and declare "the Alfa GTV is the more civilised car". He might try another pair another day and "the Fulvia is the car I'd drive to Italy and back in a weekend while the GTV is an invorgorating car for a sunday morning". Either can be lovely, either can be pigs, and my view is that the devil is in the detail and 50 years on that's more "nurture than nature".
