We chartered out of St. Vincent several years ago and loved it. Went down to Union island and back. Much better than BVI. It was around mid December and the weather was perfect: 15 to 20 knots wind, not much rain, nice steady seas (though we rolled in each and every anchorage, as predicted in most guide books). The vendors (boat boys) were never a problem and quite often were a nice welcome for the convenience they provide. Security around St. Vincent can be a problem if one is not choosing his anchoring sites carefully, but once you leave St. Vincent it is never a problem. Make sure to stop in Mayreau and visit Dennis at his Hideaway (restaurant / bar / hotel). He serves some excellent local Jack Iron (amongst other fine things).
Enjoy the trip and fair winds.
The sea, once it casts its spell, holds one in its net of wonder forever.
Jacques Yves Cousteau