We've priced it out and it seems that a rail pass will save us money. What I'm not sure about is rather or not it makes sense to make reservations for the trains while we are still in the US? We are traveling from Venice to Lake Como to FLorence to Cinque Terra to Rome and back to Venice in the beginning of June. Thoughts?
Definitely consult one of Rick's books - they all cover train travel. I believe he does recommend reserving, particularly in high season when you are going. Not sure what the RailPass deal is. I took train from Venice to Florence, booked it from home and had a reservation. No problems at all.
I suggest you do as you are taking all the popular tourist routes. I travelled from Florence to Genoa in March and the train was full and the same from Bologna to Venice 3 weeks ago and this is not their peak season. Also depends what class you want to travel but if your time is pretty tight it's worth reserving a seat.