Re: St Maarten itinerary - 9 days
Saba was my first thought too.. And it's possible to be picked up at the bay near the moorings (Wells Bay IIRC).. It's a bit of a trick landing a dinghy there though. The drive up out of Wells is worth it!
You'll not find a more unique place in the region. If your group is fit climb the 1000 steps at Windwardside to the tropical jungle at the peak.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)