Yeah, RC doesn’t attract the boozer crowd. There are cheaper cruise companies where you can drink yourself blotto 🥴
You already got some advice but I’ll jot down mine here.
Rome is about one hour from the port. But definitely worth a day trip! If you book excursions through RC, and it’s late coming back, they will guarantee you’ll get back on the ship. But RC excursions are always more expensive than the private local ones.
Naples, as already stated, you can just walk to the city as it’s right by the port. Head towards the Centro Storico area, not the main train station. Naples is a very marmite city, I personally love it, been three times and wish to go again. But it’s very hot and smelly in summer.
While there you could do a day trip to Capri but it’ll be very busy there too. Or Sorrento depending on how much time you have at port. Pompeii and Herculaneum are very interesting and can be easily visited by train from Naples. But again, very hot and you are likely starting to wilt after one hour..
La Spezia, I can’t advice as I haven’t been there.
But honestly, no need to worry, you’ll have a great time. Just make sure you do some planning! I know someone who went onto the same cruise after us, didn’t plan at all as they thought they just swan out and mooch a bit. They missed out a lot.