I've been to the Vista Spa twice.... the first time was a cabana massage on
Castaway Cay during PCC 1.0 and it was great. The second time was on a 3 day cruise family vacation last summer. Each day in the Navagator, there's a spa special and I booked the special for the Castaway Cay day. It may be offered on a different day, but it included a full body sugar scrub and massage for about $100. The second experience was much more spa like than the first, because the first was on the island about 10 minutes after Mike asked me to marry him.
I don't know if they post the spa specials somewhere in the navagators online, but they are certainly worth keeping in mind. I have always found flexability in the Vista Spa schedule once on board.