This seems like it would be a useful talent, up until you realize that if you're affecting more than 4-5 NPCs (and often fewer than that) one of them is guaranteed to make their save and ruin the entire effect.
Short of trying to play with a crazy high CHA bonus (to boost the save DC), are there any tricks I'm missing for making it more effective?
A couple of ideas:
1.Harmonic Sage Feat
2.Prima Donna ability of the Chelish Diva archetype