What kind of society do you wnt to live in? One that is stuck in old hierarchies or one where upward mobility is a realistic option? The answer is a no-brainer and I always enjoy studies that find that people at the top came from all sorts of backgrounds -- including all sorts of universities.
I expect that these days, attendance at an elite institution may be good for entree (cheap screening by employers), but quickly fades. After a while, it's "what have you done for me lately?" It would be great to have international (as well as intertemporal) comparisons, but the empirics are difficult.
Here is a study that looks at the evidence from Israel. (H/T Freakonomics) As hoped for, the data show that elite diplomas are good for entree, but you cannot fool the market for long; it (competition) is able to draw deeper conclusions after not too much time has elapsed.