Do we really need to purchase this before we leave? Now that Trenitalia does not take US credit cards, the rate offered by Rail Europe ($100 more)is not applealing. Can we just get them when we arrive in Rome? There seem to be several of the direct trains.
Grant, generally not necessary. Depending on how many are in your party, you may have trouble getting seats together. I was just on the Eurostar AV from Rome to Florence (and vice versa) about 2 weeks ago. There were 4 of us, and while we did not get 4 seats at the little table together, we were across the aisle from each other - and depending on who's around, you could probably convince people to move around so you can be together...
We bought Rome/Florence an hour before the train. We bought Florence/Rome two days before.
Bottom line, i suppose -- you won't be left behind, you just might not be sitting together.
Enjoy your trip!
Buy your tickets when you arrive in Rome. Amica fares (20% discount) are offered on fast trains. If any of the allotted seats are still available, you can get an Amica fare up to midnight of the day before departure.
You won't have problems getting seats. Getting seats together could be an issue if you have a group of people but you usually can get seats. There are 51 trains a day from Rome to Florence. Each one holds as many people as a 747. Most runs are Eurostars. Most are non-stops. The fare is 36.10E on the Eurostars. About 27Euro for the ICPlus trains (they do make some stops). The trip takes 1hr. 40min. on the Eurostars. You stand the best chance of getting the tickets you want by buying your tickets when you first arrive in Rome. As Tim says above, you have a chance for the limited AMICA fare.
FYI - Trenitalia strike scheduled March 14 starting at 9 PM until 9PM on March 15! Schedule accordingly!