There are two schools of thought with the V6 cambelts.
1) The dreamland that is the official Alfa interval of 75,000 miles/four years
2) The reality, that over about 55,000miles the risk of engine destruction from cambelt failure increases quite considerably.
That is not to say that many V6s do not get to 75, cos they do, or that no V6s have cambelt failure under 55, as occasionally they do, but in the generality there have been a comparatively higher number of failures in the 55-65k region.
As cambelt failure often means scrapping the car, then it is to be avoided if at all possible by timely maintainance. If however your car has a full Alfa dealership service record and the belt fails before 75/4 years, then Alfa will usually foot the bill, but don't count on this in the current economic climate. In any event prevention is far better than cure.
Also don't forget it is advisable to change the water pump, and compulsory to fit a new tensioner. Any cambelt rollers with dry/rough sounding bearings need changing as well. If your heater is crap, then put a thermostat in as well..but thats nothing to do with the cambelt...