You need to understand that you will not be able to see "all the major things" or even a large portion of major things (whatever that means). We have spent months in some of these places and have yet to see everything. You need to do your pre-cruise homework on each port and than make choices. The internet is a good source, you should read about the different tours offered by your cruise, and we also like to spend some time at a large bookstore such as Borders just reading through some of their travel books (many think Rick Steves is one of the best). We know all these ports, with the exception of Tunis, very well and could probably write you a short book on each port. The choices really vary in a big way. For example, in Ajaccio you could simply walk to a nice beach and enjoy lunch in town...or you could take a long bus tour to the Calanches and see some interesting geological formations (totally different ways to spend a day). In La Spezia you might want to read about Cinque Terre which is a different kind of option than going to a large busy city such as Florence. You can handle all of these ports on your own (with the exception of Tunis) if you do your homework. As to Tunis, we think this port is best seen on a tour for at least 1/2 day. It is possible to walk from the port to a nice beach in Tunis, but I recall my wife having several thousand eyes watching her every move when we walked to the beach and she was the only western woman wearing a swim suit (the locals all wore long burqa-type garments). You have a great itinerary so let the homework begin!