How does it affect tourists Peter? I assume that the authorities have no way of knowing if your car is compliant or not if not Italian registered. And historic car events such as the Mile Miglia.....do they have special dispensation?
I often ask myself that very question. When particular restrictions are in force, such as periods of high polution, visitors would not even know about them.
As for the Mile Miglia, it is possible that they don't pass through restricted areas but even if they did any event involving historic vehicles would have exemptions.