Performance came into it because of the issues regarding stress. If a part isn't performing corretly due to stress e.g. larger wheels, wider wheels, wider tyres then it is an issue worth noting.
From a performance point of view there is no need to run anything more than 15x7's with 185 possibly 195's at a stretch (I wouldn't put 195's on anything less than a GT/HGT as it's dead weight). I've had more wheel, wheel size and tyre combos that I can count on my fingers and toes and 185/55, 195/45 or 195/50 on 15x7 is where it's at for no compromise in performance and longevity of parts.
The only advantage is 17's as you say is looks.
Exactly...so not only are the potential problems caused by fitting larger wheels undesirable, the performance drops are too and the amount of grip you can get from wider wheels/tyres on such a car is totally excessive and not needed.
So yeah when I said I personally preferred 15s thats basically because 1. I didn't want a compromise like you say and 2. I just wanted to keep the car as original as possible but with the rarer abarth wheels so it was still abit different.
At no point did I say don't do this or don't do that.
Just bringing up all the various points to consider to help sammiboicurtis when buying his wheels so that he ends up with the right decision.