(Of course, it mainly depends on what criteria you buy into, but once you've done that, there are substantial and insubstantial pieces of music, and a vast middle, containing music that is somewhere in between.)

A lot of what I like is crap. A lot of what I admire is good, or Great, but, still, when it came time to test out a new encoder last night, I reached for "Lust for Life", and not some Great Masterwork. "Lust for Life" isn't Great Music; it's Great Fun, perhaps. Musically, all it shows is that Iggy had a tight band back then, and that he was probably a fan of Motown as an adolescent, revisiting that old love while in the early stages of recovery from his addictions. It also shows what a great persona he'd built, but that's extra-musical, perhaps, unless you're a diehard opera fan or something.

I can learn a lot about the construction of melody from, say, Tchaikovsky's third symphony, and about polytonal approaches to improvising on ancient jazz standards from a recording by Joe Henderson or George Coleman; I can learn about rhythmic freedom from studying the improvisations of a Don Cherry or a Branford Marsalis. They all do/did a Great Job at making Great Music from time to time, creating things that, musically, stand up to repeated listens and still leave more for you to discover.

I stress the word "musically", because the word "music" conjures in most people's minds the products of the entertainment industry, which contains a lot of extra-musical content, like the aforementioned persona-constructs, and the marketing (an art in its own right, but it's not music), and the technology (e.g. the audio-production suites and the algorithms that produce the ambience and effects, making anything and anybody sound slick and sweet). There is a lot to write about or study in even the lowliest, shallowest pop song, but it isn't Great Music. Arguably, there are tons of exceptions, e.g. when The Beatles, Zappa, Beefheart, and Steely Dan, et al, both broke new ground (on occasion) within the contexts in which they worked, and did it so well, that it had a lasting impact.

I'm playing an AAC of "Lust for Life" right now. Fuck art, let's dance.