So if Tolkien's literature is essentially anthropocentric, if I'm right that his biggest overarching goal was to create in the reader this sense of doomy fatalism that he saw as characterizing the Nordic mythoi and worldview in the dawn of Northern European Christianity, if his most basic project was (as I suspect it might have been) to imagine what it must have felt like to be a seventh-century Finn or Icelander, then why does he spend so much time on the Elves, and not the Men? Why Elves at all?
I don't know if I have a complete answer to this (again, the History of Middle Earth still looms on my horizon). I don't know if I know how it all fits together. But here's my stab at it.
Tolkien was a Romantic. Generationally, he was too late; he was, in point of fact, a Modern; then too of course his Romanticism was more than tempered by his Medievalist temperament. But I think it's plain to see that his sense of beauty is straight out of the post-Romantic fairy stories and illustrations of the nineteenth century. His is a pre-Raphaelite sensibility, if you like. I probably can't characterize it more exactly than that, but I'm sure somebody has.
I think his Elves, and by extension The Silmarillion as a whole, are his attempt to imagine as fully as possible a world and a race of Beauty, as perceived by a pre-Raphaelite sensibility. Elves are, above all else, beautiful. At every turn in Tolkien, they're held up as the standard of beauty; even their flaws are above reproach, really, because of their beauty. And there's really no split in Tolkien between truth and beauty. Truth=beauty, beauty=truth, as much in Tolkien as in Keats. At least as far as Elves are concerned. Elves' bodies, their songs, their homes, their language, their eyes, their trees, their armor, their everything is beauty itself. And so is, thanks to the Silmarillion, their creation story: it's like Genesis rewritten by a pre-Raphaelite, all song and twilight and glowing trees and whatnot.
So Tolkien is all about trying to capture this beauty that, in his day, was really out of fashion. But in a sense, what could be more Modernist (and at the same time medieval) than his decision to locate that beauty so determinedly not in Men? Once Tolkien has grasped beauty, it's like he can't bring himself to imagine locating that beauty in Men. Men are too weak - if the 20th century taught us anything, it was that. If beauty is going to be in the world, it has to be in another race. A race that Men can't hope to emulate, and are usually too dull to want to.
This is Tolkien's aesthetic: mankind quaking in the presence of beauty, as much as basking in it. It's the ability to perceive beauty but the inability to join with it. It's Man being fundamentally cut off from beauty, isolated, whether by nature or (as I thought here) by age. It's not quite loss, although Tolkien's literature is permeated by a sense of loss; it's not truly loss because Man never actually possessed beauty, was never in communion with it; that's the province of the Elves.
Again, it's a commentary upon the human condition. I keep coming back to that. Most of his literary energies were spent on trying to capture this beauty, but I think it was essentially in an effort to show us humans what we're not and can never be. That that is our lot.