Culebrita, especially Bahia de Tortugas, is indeed magical and my favorite bay in the SVI/USVI/BVI. For an equally remote feel, I head to the south shore of Vieques.

I think the next best option is the south shore of St John - both Salt Pond Bay and Little Lameshur Bay have nice sand beaches with excellent snorkeling and are relatively uncrowded. Also they will be unaffected by the north swell common in February.

On the north shore of St John, Leinster Bay is well protected (especially if you can get one of the inner moorings) with a remote feel and a decent beach, nearby snorkeling at Waterlemon Cay, and short hike to Annaberg Plantation ruins. Nearby Maho Bay and Francis Bay are also well protected in almost all conditions and have great beaches, lots of sea turtles, and plenty of mooring balls.

Around St Thomas, you have a nice anchorage at Buck Island just south of Charlotte Amalie that is usually deserted after 3 pm. No sandy beach but good snorkeling and great sundown views. Christmas Cove at Little St James Island is similar. Brewers Bay near the airport is extremely well protected with nice beach and snorkeling.