I am seriously late to this party (EIGHT PAGES? Really, people? laugh ) but I have a few thoughts:

1) As many have noted, the Ivies and their ilk are selecting for future political, corporate, and social elites, not future intellectuals. There ARE still schools selecting for the latter, and most of them are SLACS. (There are some bigger schools as well, e.g. my impression is that MIT is one.)

2) That's what the Admissions people at the Ivies care about for admitting undergrads (which I realize was the original point of this thread). But it's not neccessarily what the intellectual atmosphere of the place is, what the faculty care about. (Although, the weird mixed bag of ego and real scholarship among the faculty at those places is another whole topic, don't get me started.)

3) COHORT MATTERS. The difference between a large state school and a smaller more elite place amounts to this: What the professor can teach is limited by the overall intellectual capability of the class as a whole. Intro Botany really is different at a school that overall has smarter students.

4) How to find "one's people"? There's no getting around the fact that students at any good school are going to be relatively privileged. But some schools have different cultures than others, and some tend to attract quirky individuals, deep thinkers, and other non-HYPS characteristics.

5) Bostonian, I agree with you that there are real individual differences in intelligence, and that it matters. But you should know that The Bell Curve is full of garbage science.