Good story Dogdaze - a nice stitch-up.
We flew into Rome Ciampino some years back. Picked up a free bus to the Train Station, then just a cheap time limited commuter ticket, that lasted just long enough to get us into Termini/Rome Central Station, then out to our Hotel near St.Peters. Cost peanuts & proved OK as they passed inspection.
Whilst we have never actually attended Mugello on race day, I thought I would chip in with a few basic thoughts. In my experience Italian trains run pretty well. However the ticket halls can get very crowded, with some enormous queues & I think this is where the problems can start. My advice would be to purchase the rail tickets in advance & nominate carefully the day of travel & time of the train - it is probably easier to do this at the ticket machines, which are multi-lingual & take cash/cards. You will find the locals like to press/push/shove - all part of the experience. The track up to Borgo threads it's way up the Sieve river valley, so hardly a quick run. Just get Google to do the calculations - obviously needs an early start. I'm not sure whether they put on any extra trains for the event , but the rail company, or maybe the circuit can provide details. Behaviour at the track is............. interesting, verging on bonkers. Noisy, very 46 yellow & enthusiastic. Some guys even take bike engines along on sleds to the campsites, only to rev them on the limiter until they blow..... why?
Anyway I have to confess, whilst we had intended to go & we did loads of research/planning, we got ourselves talked out of taking the bikes by some buddies who had attended the year previous. They suffered some petty thieving, which was annoying when that far from home, as well as problems getting out of the circuit after the race. Hence we considered using the train, like you, so looked at all the options. Eventually took the bikes on the Ferry to Spain & watched the races from the comfort of an armchair instead. Sad really. Hopefully someone on the forum from Italy can help with some first hand experience.
Anyway, enjoy & take care ........................... KEN