Well, as I said in my other comment- almost any cleric or wizard has a use for this, as most of those guys get a spell like ability that could benefit immensely from being extended, quickened, some even from empower for things like a dragon sorc's fire breath. Don't get me wrong, it's a niche as hell trick, but as a Luck/Travel domain cleric, I look at some of the other domains and honestly think of switching deity. For example,

Touch of Law (Sp): You can touch a willing creature as a standard action, infusing it with the power of divine order and allowing it to treat all attack rolls, skill checks, ability checks, and saving throws for 1 round as if the natural d20 roll resulted in an 11. You can use this ability a number of times per day equal to 3 + your Wisdom modifier.

Use Divine Metamastery to apply a Mythic Extend on each of those you use in combat, and soon you have a whole team who aren't even rolling dice- they're just scoring hits against all but the really nasty AC enemies. Apply a quicken rod to that, and you can have the whole team buffed to the nines in two rounds.

Or...

Vision of Madness (Sp): You can give a creature a vision of madness as a melee touch attack. Choose one of the following: attack rolls, saving throws, or skill checks. The target receives a bonus to the chosen rolls equal to ½ your cleric level (minimum +1) and a penalty to the other two types of rolls equal to ½ your cleric level (minimum –1). This effect fades after 3 rounds. You can use this ability a number of times per day equal to 3 + your Wisdom modifier.

Apply Extend from BoF, six rounds, and a Mythic Empower... at level 20, you just debuffed an enemy with -17 to attack rolls and saving throws. +17 to any skill check he wants to make, but that guy has to survive on skill checks alone for six rounds while trying to avoid any attack/save.