Hi CandJShaw, welcome to CruiseReviews! You'll love the Valor! We sailed on her last May, but not that itinerary. We did the western Caribbean on her. We booked our excursions through the ship before we left, just booked on-line. You can do independent tours, but I prefer taking the ship's excursions to locations I've not visited before or do not feel comfortable with doing my own thing.
I totally agree with Jim, San Juan is a great walking tour. Old San Juan is alive with history and the Fort and Cathedral are so close, that walking is fine with me. St. Thomas we've been to many times, so usually take the ferry over to St. John and a cab to Trunk Bay. Trunk Bay is one of the top 10 beaches in the world, great snorkel trail about 50 yards from the shore, and all the ammenities you need. St. Thomas should be visited, though, great for shopping. Coki Beach and Magen's Bay are two of the more famous beaches. Sapphire beach is good for snorkeling, but doesn't have all the ammenities.
Half Moon Cay is absolutely my favorite private island, it is amazingly beautiful. Definitely a beach day there. Snorkeling is decent, as well.
Grand Turk was hard hit by the hurricane a couple of years ago. It's a flat island, but very clean and very friendly. We did a snorkel through the ship when we went that was really great, crystal clear water. There's a shopping area where you dock, as well as a very nice beach. I've heard great reviews on the segway tour there.
I know you'll enjoy the Valor, she's an easy ship to navigate. Be sure to try the chocolate melting cake, at least once. Hope you have marvelous weather, calm seas, and a fantastic cruise!