It's always worth doing Bounty Hunter. But since everything on Mirage is slightly boosted, so is BH.
There are 3 variants of Bounty Hunter quests. There's a random one each day (it resets at 12AM server time).
Moreover, all bosses drop Mirages. Always. No quest required.
* 2-5 Mirage Celestones from Serp, Nox, and Turtle