I really like your idea regarding the tangible/intangible focal point of certain art forms. Never really thought of it that way before.

On the other hand, I gotta disagree with your main point, however nuanced, in regards to the inherent potency of a dated work of art. Might come down to a fundamental disagreement about what art is. Not sure. But I'm of the impression that it's not so easy to conflate cultural norms/public opinion with the impact of a work. It'd be really easy to apply cultural relativism to art, say something along the lines of "this is beautiful to you at this time and that's fine, but it's not beautiful to me and thus not inherently beautiful, only culturally so." But that's kind of a cop out, isn't it? Each culture in each era uses its own language, in both a linguistic and cultural sense, to describe the world it interacts with. Just because I refuse to learn that culture's language doesn't sap the inherent beauty from its native art. At some point, that Sumerian or whatever love poem struck at a fundamental aspect of love/happiness/material wealth that might just be inherent to the human condition and the way we classify the world, no matter what era we live in. So the onus falls on us to learn the language and parse the inherent beauty from an artwork, it doesn't fall on the artwork to make eternally apparent the beauty behind that first generative idea.

Or maybe that poem was a joke, or doggerel or something. "You make me happy even without beer" still sounds pretty close to the mark. Is there anything to suggest it was an important work, or is it just momentous because it's really old and still legible?