We are booked on a mediteranian cruise this summer stopping at Civatechia (Rome), with the next stop in Naples. Given the distance from the port to Rome, is it feasable to grab a hotel in Rome, and hop on the train to Naples the next day? We figure this will be the only time we'll ever be in Rome in our lifetime, and will ease the push to see more and make it back to the ship in time.
No problem at all; just tell the ship that you are going to do this. However, make sure your timing works out. Italian trains aren't the most reliable. You will gain a day in rome at the expense of trave time and miss out on Pompeii, Amalfi, or Capri.