Well, we ended up not doing the dune buggy excursion. They changed the age limits so we couldn't go. But the other folks in our group did the 4 hour ruin tour (sorry..I forgot the name) and said it was gorgeous. The only downfall was that it was a mile hike in between the 2 ruins you saw!!! Some other people we met did the Corona Beach and they had a good time!!
We ended up taking the double decker bus tour and then wandering around down by the beach. Since we had a little one, we headed back to the boat really early!
I hope ya'll have fun on your cruise!