I am going on your cruise. My roomate did this same cruise in fall of 2003 so is quite familiar with the itinerary and she has travelled to Greece many times. From what I understand, the Greek Isles are all very easy to do on your own, as well as Dubrovnik. I am thinking of taking a ship shore excursion in Naples, since I've heard it's the only way to see both the Amalfi Coast and Capri. My roomate did a shore excursion in Turkey and loved it....she wants to do the same one again.
I am just now starting to research all of this.
Feel free to email me and we can talk more.