I gotta say, I don't buy the "factor of age" thing one bit. If there's one thing I've noticed about those who I know who are the biggest converts to 4E, we tend to be of two demographics:
1. Old-timers like me (vintage 1980!), who drifted away from the game since Red Box/RC era, find 4E a nice mix of robust rules with improvisational freewheeling attitude, and welcome the lack of setting focus and loss of decades of rules-cruft.
Vintage 1980 here too. Nice post, really, and captures what (I think) appeals most about 4E to older players: the streamlined mechanics, and the ease - especially for the DM - to run this thing fast and loose. For me, 3.5 was the complete opposite: prepping a session for 3.5 was careful drafting. I enjoyed both, and continue to enjoy both. None of this, however, has to do with "a welcome lack of setting focus". 4E fluff exists, and it sucks, big time. Which I take as a big incentive to come up with something better (read: "something more suited to my own taste"). More on that shortly.
Jeff, having read your original post, I'd like to recommend you to try to take on 4E like I do, which is as follows. You are right, you stopped being a completist, a guy who (to use Psion's terms)
bought at least one WotC supplement a month. You know, buying one hardcover a month doesn't strike me as very old fashioned at all. The great appeal of D&D is, and always has been, to work with a minimum of official stuff and make the game your own. That, in my estimate, is the everlasting appeal of the Red Box and old Greyhawk box with two 30 page supplements. It's playing D&D before you got your crunch from official splatbooks, and before there was
canon.
For me, 4E has been a liberating return to that time, precisely because 4E non-core products suck so much. 4E adventures are seriously uninspired and lacking in roleplaying, their splatbooks completely pointless rehash of extant mechanics - and guess what, I feel
liberated. I don't have to buy every book anymore, I am free to go with 4E where I want,
because I know WotC products no longer appeal to me, operating as they do on design principles which target an audience I'm no longer part of. And that is a fact I treasure as much as I did its opposite when playing 3E (which I still do as well). For this is a freedom I never had with 3.5, when collecting stuff kicked in early and both DMs and players expected every little thing you bring to the table to have come out of a WotC book.
So the best way to enjoy 4E for me - I guess, the only way - is to take the excellent core books they produced, sidestep their laughable marketing and pitiful "follow up" products, and make their beautiful game my own. That way, I couldn't care less whether I'm in their target audience. I know I'm not, and I can still feel proud playing 4E.