While Frenchmen's Reef is a nice hotel (although it is in need of, and getting, an upgrade), it is not an efficient location for using points. A week there in March will cost 210,000 points without a view. If you want to see the ocean from your room it will cost an additional $110 a night.
For 180,000 points you can stay at the J.W.Marriott in Cancun, one of the nicest hotels in the Marriott chain. The airport and surrounding area are busier than St. Thomas but the hotel shares facilities with the Marriott Casa Magna. That gives you access to half a dozen restaurants, two pools, an outstanding spa and a long stretch of beach. You don't need to leave the resort to have an excellent vacation.