To be honest, I prefer seeing idioms. It tells me that the user has a grasp on the elegance of the language. But I think that's completely orthogonal to "cleverness" - at least in the usage seen here. Idiomatic can be clear, clean, precise - and can be all these things while still being flexible to handle changing requirements.
I'll definitely agree to the "simple, obvious, correct." But I don't think idiomaticness has anything to do with that.
Then again, I've managed to eliminate about 80-90% of my manager's code from our department, and significant portions of his design. His design often is "simple, works, and rigid." I've replaced most of that with "simpler, consistant, flexible." At least, in my not-so-humble opinion ;-)