Hi Harv, Brogins back from a nice week vacation in Italy... with no-wanted connection to the web!!
Well, the guys above have described quite well the Hell scenario that Mugello can present in the three days for the motoGP. It is not going to be easy...
The way that me and my friends from Florence center usually approach race day is:
Decide which Van to take (we all race motorcycles..)
Fill it with 50cc Scooters (everyone has a scooter in Florence..500.000 people, 300.000 scooters/motorbikes - seriousily) and people (by law max three people in the front, on race day we managed three in the front and four in the back with 4 scooters)
Drive the van up to SAN PIERO A SIEVE (20 minutes or less from the track)... Park the van, take the scooters and ride to the track.
The scooters better be to be able to go offroad, to get out from the circuit after the race not only on tarmac as the traffic of bikes is orrendous. Of Course we race each other to get back to the van and the last couple (usually couple, as we are all riding two people on the scooter - illegal ) - pay the dinner...

:lol
If you are planning to stay in Rome, it is impossible to travel on race day. Well, it is possible, but is going to become a nightmare trip. Rome Florence by car are three hours. Florence - Mugello not knowing the road and using the motorway another hour - These time are in normal days - In race day it is impossible to forecast any travel time around the area.
That's what I would do...
http://www.ecomoverent.com/scooter/Scooter_250.asp You can rent a 250cc scooter... confortable for two people for the weekend and able to do 130KM/h (max speed 155Km/h, 160..) on the motorway no problem. You leave on saturday from rome and you take it easy to Florence doing some tourist things too. You can find a bed and breakfast near Florence or in Florence (not bad idea where to spend the saturday night) - I can help with some suggestions) - On sunday morning you wake up at 6 am and you drive the scooter to the circuit - you can buy the ticket on line now even at Ducati.com (for the place where to sit and see I agree with the comments above.. ) - On the way back... you have more than 300Km to do on a Scooter to get back to Rome on Sunday..hard but duable..
Well, if you decide to stay in Florence instead of rome.. all become easier and you need to find a scooter (even 50cc) in Florence.. U2U me and I will tell you where.
See you soon as soon stop to rain.... well was 26 degree sunny in Italy this morning!!!