The LA-assignment thread: Making monster PCs VI-able

[TiaC]

You can boost SLAs by up to 4 levels (up to a maximum equal to your HD) with the Practiced Magic feat. Not sure if it would extend to PLAs under transparency.

It works similarly to Practiced Spellcaster, and can be found in the Shackled City hardcover adventure, which is technically an official product, the same way Dragon Compendium is.

This is really important as that one feat would have a pretty big impact on a lot of these monsters.

Pretty common types, mind you. And at high levels, mind blank and protection from X are going to be pretty common on the enemies you'd want to use your best powers on.
I'm inclined to think people overestimate the importance of mind-affecting immunity (on monsters—PCs are likely to prepare defenses against such), but it's still more important than you seem to be giving credit for.

Normally, I'd be with you here, but this monster has the best mind-affecting power to deal with immune foes. Dominate is stupidly powerful, and can easily get you as much as Leadership does. Minions to throw at immune foes works really well.