Dubrovnik: don't book the Brandy Tasting/Cavtat/Old Town tour if you're not an extreme brandy lover. The Brandy Tasting session, although located in a beautiful place, is far, then you'll spent a lot of time in Cavtat (it's only a photo-spot small city) and, in the end, you won't have enough time to visit the Old Town (it's a World Heritage!).
Tunis: we've been in Tunis during our last cruise. It was my first experience in Northern Africa and I didn't like it. Anyway, I gave Tunis another try. Again, we went to the M'dina and the Souk. Worthless. Princess could move this stop to another place - Morocco, for example.
Malta: we've also been there, a year ago, and we loved coming back. Our tour was for wine lovers (and we are) - the Meridiana Winery wine tasting. We brought very good Maltese wines. Wandering at the waterfront, by the harbour, for a cold beer and some souvenirs were a nice option for the pre-"back on board" moments.