John,
Having done a "grand tour" this summer, if you're going from Rome, IMHO, it might be a bit far to get to Milan if you want to actuallly get out and do or see stuff. However, Modena is in much easier reach, with the Ferrari aspects already posted, plus you are slap bang in Maserati, Lamborghini, Pagani and Ducati factory territory as well, which are all worth seeing. As part of the trip, unless the weather is completely rubbish, I suggest as a real "must" is that you plan your route after Modena back to Rome to take you down the old national road from Bologna to Florence, climbing over the Passo di Futa and the Passo di Raticosa - the old Mille Miglia route. Fantastic driving road (whatever you are in), fantastic scenery, rewarded by an awesome view of Florence as you come over the hills. Lord only knows how Moss averaged nigh on 100mph, even in a 300SLR in the '55 Mille Miglia. If you have time, there is the Mugello circuit a little to the north-east of Florence if there is anything going on there. Follow that by driving through the Tuscany hills to get back to Rome. Drink wine. Eat olives. Enjoy.
MG Mark