There are several theories and discussions on this
so no doubt will rage on
Probably biggest cause of issue with fitting larger wheels is also the other mods which are used:bang: which then can cause a detrimental affect on the accelerated wear and tear of other parts, lower stiffer suspension,hub spacers,etc.
The way i see it if Fiat and the dealers sell the wheels and fit them to various models then there cant be a huge issue
A lot of the components of the cars are the same throughout the range any way
I have also even seen the 900cc twin air with the 17"two tone wheels on (the same style as my wheels) as a factory option
I have a 1.2 8v not noticed anything untoward other than the steering is slightly heavier due to the wider wheel/tyre and mpg is very slightly less again wider wheel/tyre.