I think part of being intelligent as a lyricist is understanding the medium well enough to know that good lyrics aren't necessarily "smart" lyrics. For that matter, they need not be lyrics at all. A yelp or a sigh in the right places can be just as effective as a polished line. So, for me, Morrissey is the finest lyricist. Not because his lyrics make me think of Byron's poetry, but because he combined the best of a bookish sensibility with amazing pop instincts.
Other "smart" lyricists I would put up there would be Robert Forster, Grant McLennan, Bob Dylan, Chuck D., and Lennon/McCartney.