Cruz Bay isn't as convenient for visiting boaters as places in the BVI. It's a longish dingy ride for 6 ppl to/from Salomon moorings, esp for nitelife activities. There's rarely any place to anchor in Cruz Bay and the moorings are private. If you grab a ball at Caneel there's taxi service to/from Cruz Bay so that's what I'd do.
On the other hand, St John beaches are beautiful. Our favs are Maho, Waterlemon and Lameshur.