I'm open to bumping up Concentration, Spellsight, and Intimidate from niche to common, but am not quite convinced yet.

When I think of categorizing an effect, I think of build posts on the forums. Not necessarily endgame build posts -- though those do loom large as the most significant percentage -- but any build. Specifically builds which list gear.

Monks using concentration is on par with bards wanting perform: The definition of niche. But can you find any non-monk build posts that list gear which includes concentration? It doesn't have to be a crafted effect; even if it's just part of a named item, that counts in my book.

Same idea for spellsight and intimidate.