Sorry Flynn, I didn't do a very good job of explaining what I though was wrong here. To me it's just a grammar issue. How the Feat is worded makes it possible to read the feat incorrectly. I'm sure most will get the correct interpretation, I did, it's just it could be construed another way.
So as it reads right now. Favored Enemy Spell (Mystic, Scholar). It reads as if this feat works for your enemies favorite spell, not your own for use against said enemy.
If you write it this way Favored Enemy: Spell (Mystic, Scholar) or Favored Enemy - Spell (Mystic, Scholar) Then it reads more clearly. Now it reads as a variant of the Favored Enemy feat. It's just a nit picky point of grammar is all.