Most things improve a very specific ability's bonus rather than generally making bonuses better but there are too exceptions, Ability Enhancer & Fell Energy.
Both are Dragon Magazine, Enhancer only works on Ability-related bonuses and Fell Energy works on everything but requires you to be Undead so I'm sure you can see the problem with that. In theory through, they might be something out there that the Mind-Affecting bonus piggybacks a main effect Undead are not Immune to allowing you to Fell Energy it and Polymorph out of the Undead Type for an increased bonus.
