On a different note, rather than the sky lift, ask a cabbie to take you to Drake's Seat. I've been to Drake's Seat (and farther up to Mt Top) several times and it is beautiful. I've never done the sky lift, but from others I know that have, they prefer Drake's Seat and it is less expensive.
I think St John has some beautiful sights and snorkeling, but it does take a while to get there and back (allow 2hrs or more in total), but the trip is scenic also. The beaches on St. Thomas are also beautiful. All in all, I prefer the snorkeling on St John, but the snorkeling at Coki, Sapphire, and Secret Harbor are close seconds. It really comes down to whether you want to spend that much time in transit to get to/from the beach.