Dave, I am going to turn your question around. Do you ever think you will go to Grand Cayman? That is where I would recommend an Atlantis submarine tour. As far as the tram, I would wait until after you have had a chance to do other things in St. Thomas; beach at Maegan's Bay, taxi tour to Mountain top, ferry to St. John and of course shop till you drop. A relaxing ride up the mountain is just he thing to finish your day in St. Thomas and the sun will probably be lower in the sky for good photography.
Bon Voyage