In Dubrovnik it's absoluteley unnecessary to book an excursion. Last week I have been ther e with Costa Mediterranea. The ship was just 5 minutes outside the harbour. The tender boats landed direct in the middle of the old town. There you have every possibility to to explore the old town. For 7.50 Euro you should buy an admission for the top of the city wall. The views you have over the town and over the sea are worth every cent.
In Rhodos we had time from 8a.m. to 6 p.m. So we took a little Fiat Panda for 50 Euro from the rent-a-car station direkt at the harbour. We have been the first tourists in the Valley of the Butterflies. No buses had arrived yet. So we really could enjoy this romantic valley on our own
In Lindos we met all the tourist and all the donkeys. But with a car we could leave at our own decision and did not have to wait, until the last bus tourist had found his way back.
So we had time enough for a sunbath and swim on a secluded beach, before we geve back the car at 3 p.m. A walk through the old town of Rhodos ended a day, which we have organized. Far better than letting other people organize you!