I haven't been to Spice Mas, but have been to Carnival on Carriacou many times, (going back in March) and if it's any indication it should be a great time. The advice I've seen is to book early as the most popular properties go quick. There should be a trip report from Carnival this year in this forum.
Not much can compare with a charter through the Grenadines, absolutely beautiful.

Drink all day at home, your friends worry about you; do it on vacation and they say "what a good time you're having". Save your friends needless worry, travel more!