The America's Cup Racing is a hoot! We did that a few years ago. A bunch of tourists maning a sailing yacht. I was just a cheerleader, but my hubby was cranking on something. We lost by just a hair, but it was great fun. Don't waste your money snorkeling, it's not that good there. There is plenty of shopping near the port.
I haven't been to St. Croix in years and years, but have heard it hasn't changed much. The last time I was there I went diving/snorkeling. St. Thomas is really better for shopping, unless they've changed, St. Croix was more expensive. Hope this helps a little.