My wife and I will be travelling a few legs in July and didn't want to commit to a set train 4 months ahead of time and realize we would lose some cost savings. But our question is, will there be a poor likelihood that we could find seats next to each other if we buy them at the station an hour before the train is scheduled to leave.
Our travels I assumr will all be on trenitalia going from:
Naples to Rome
Rome to La Spezia (Cinque Terra)
La Spezia to Pisa then Florence
Florence to Venice
In July, an hour before departure, you may/may not find seats next to one another but you can probably find them on the same car. If you are willing to be flexible about your travel classes or departure time, this increases your chance. If you were willing to purchase them a little sooner (earlier in the day? the day before?) it would be more of a guarantee. I am basing this on my travel last June with a group of 4. We purchased a lot of tickets last minute on popular routes (Florence/Rome, Rome/Naples). One train we were all next to one another. Another train, we sat 2 together, the other two separate. The last train, we were all separate but on the same car. On the plus side, I had very nice conversations with my seatmates.
The likelihood is greater in first class, but the day of or the day before should not be a big problem. I occasionally found discount tickets still available at the train station on the day of travel.
Even in July the probability of not getting two seats together is very low. Getting fours together does complicated it but getting two together has never been a problem for us in our of travels. Unless you are hitting a special holiday or a football game somewhere, the trains are never packed. Some of the trains will be Regionale trains with no seat reservation. Then you just have to find a seat.
worst-case scenario: You might always try asking the person in the seat if they wouldn't mind trading with you or your spouse so you could sit together. People have done that on planes a number of times, and fellow passengers are usually willing to accommodate the request.
Florence to Venice is the only leg that in July might be a bit more crowded on the early morning trains (lots of tourists take those trains), if you buy the tickets 10 min prior to departure. But if you buy them the day before, there will be no problems.
One thing you will notice is that Italian passengers (including yours truly) don't follow rules (how surprising!) when it comes to sitting at their own assigned seat. They might choose the car they are booked on, but they often sit wherever they happen to want to sit until the holder of that seat comes in and kicks them out. That will happen only if the owner of the seat is a foreign tourist, because if it's another Italian, they'll just sit wherever there is an empty seat nearby. So just do as the Italians do. Sit next to your wife and see what happens.
Sundays are the busiest time to travel on trains.
In one experience of buying tickets in the train station for the next train leaving, I could not get three seats in the same (cheapest) compartment for myself and my parents, so I paid an extra €10 per person and got three together in the next class of service. At the time, that was easiest solution at the ticket machine in Bologna, since the ticket windows had fairly long lines. The faster trains in Italy now have several "classes" or seating areas. Between Rome and La Spezia, there are fewer direct train departures per day, so if you're ready to commit to one a couple of days ahead, you could buy it at the same time you buy the Naples-Rome ticket.
As it has been point, Sunday afternoon is the busiest time on long range trains; I would add that the last weekend in July is usually quite crowded. If you have to travel at these times, you should better reserve a few a day in advance.
