We did the Barcelona to Rome last June. We only did one DCL excursion which was in Marseille. The cattle call feel of it made me very glad we didn't have any other DCL excursions booked.
In Villefranche we walked to the train station and took it to Monaco on our own. We went to the Oceanographic Museum, which we enjoyed, but Monaco was really not our thing. I wouldn't go back there. My daughter and I would have been perfectly happy just strolling around Villefranche and playing in the Med at the little beach there.
In Genoa we went to the Galata Museo del Mare. The DCL shuttle bus dropped us off right in front. We really enjoyed the museum and it had a lot of hands on activities for kids. We walked back to the ship because it was really close and we didn't want to wait for the shuttle.
In Livorno, we had booked Tuscanybus in advance to Pisa. The DCL shuttle bus drops you off right where you get on the tuscanybus. We went to Pisa and had pre-purchased our tickets online to climb the tower. Doing this on our own saved us 100s of dollars over DCL's excursion.
In Pompeii we were going to take the train to Pompeii, but we didn't dock at the main dock, so it was complicated to get there. So, we ended up paying for a shuttle at the port to take us to Pompeii and pick us up afterward. It wasn't very much money. We used Rick Steves audio Europe to guide us around Pompeii (free app for your phone).
Since we ended in Rome, we spent 3 days there seeing everything we wanted to see on our own.