My cynicism aside, there's now a convincing and serious canon of writing on the subject. In N+1, James Guida reviews books by rappers, including Jay-Z's Decoded:
To Jay-Z, rap doesn’t just happen to talk about hustling: the two roles naturally converge. Both emphasize adrenaline, language, liberty from societal constraints, and a high-stakes psychological education in sizing up people and situations. And of course there are the spoils. Few other emcees present selling drugs as such a high-flown adventure, worthy of endless, detailed elaboration. Given the ubiquity of the subject throughout the genre, this is saying something. It’s always been evident in his best lyrics: “Hope you don’t think users are the only abusers, niggas, getting high within the game/ if you do then how can you explain, I’m ten years removed and still the vibe is in my veins.” But Jay-Z is explicit about this in prose, examining his time dealing and everywhere linking it to the lines of his songs.On rap as poetry:
In Decoded, Jay-Z reveals himself as an unlikely hip-hop statesman. He likes acts both old and new and from all over the country. This catholic view helps him make the case that rap is rooted in tradition. But is the tradition chiefly a poetic one? “Rap is poetry,” Jay-Z says, “and a good MC is a good poet.” Clearly the music is a monster of living vernacular, and has plenty in common with poetry—besides rhythm and rhyme, there’s a love of phrase, simile, and metaphor. But rap is also preeminently oral, sharing qualities with acting, storytelling, and the high arts of bullshitting and invective. It makes more sense to locate its roots elsewhere, in street corner talk, toasting, and other musical genres. The music critic Kelefa Sanneh, reviewing Decoded in the New Yorker, captured the problem nicely: “Sure, he’s a poet—and, while we’re at it, a singer and percussionist, too. But why should any of these titles be more impressive than ‘rapper’?” In other words, why the need for literary prestige? After all, rappers enjoy collaborations, gatherings on boats, and the right to squash foes real and imaginary and pun all day without reprisal. And let’s not forget the heart of it, the exaltation of sailing endlessly on a rhythmic current of speech. If Jay-Z wants to be thought a poet, many actual poets would probably jump at the chance to switch places.