At least at the graduate level, the Ivies aren't necessarily the best choices. When it comes to undergraduate education you can generally assume that they are generally very good, but that maxim doesn't hold as you start getting into more and more specific subjects. If you're looking to become a quantum physics researcher, you'd be better off going to a Berkeley or MIT as opposed to Yale. And as you said, they may not even offer your particular subject.
I mean, I guess there's some appeal to saying "Oh yes, I
did go to an Ivy League school" as you gently swirl your brandy snifter, adjust your ascot, and dust off your monocle, but it's not really worth the cost and frustration just for that.
Besides, the Ivy mystique wears off after about three weeks when you realize just how much work you have to do