Thank you for your replies everyone. I think I'll just pay to get this off the table, although I still think the violation is so minor that it it absurd to charge for it.

Let me provide some more details:
- the car is a company car that my employer provided to me for permanent private usage (four years)
- it has a German licence plate
- the car will be replaced in early summer 2014, I don't expect to drive it to Italy before that
- the speeding ticket was issued by the city of Livorno, not by any national authority in case this makes a difference.