We visited Fort Zachary Taylor really just for the beach. There is not that much to see concerning the fort but the views from the top are great!
In all fairness we did not go on the Ranger guided tour so if we had, perhaps the fort would have been more interesting. But having seen other Southern US forts, this one did not have too much appeal.
The beach was nice but very rocky; it helps to have swim shoes. I would skip this all together and drive the 37 miles to Bahia Honda if you are looking for a great beach experience.