I can't help with Mayreau or Canouan, except a lot of people mention Rightous Roberts on Mayreau. Union Island has plenty of good spots now that the kite surfing school has taken off. Bouganvilia is nice, the pizza shop near the fruit market, Sparrows on the north side of the island is a great place to spend the afternoon, great beach and good food.
Goaties on PSV, but it is expensive, we usually dingy over to PM and find something local.

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!