pinic_lightning, I'm in a similar situation, only one PhD offer (actually, I've only got one offer, and I'm on the waiting list for a master's program...in another field), from a top 50, but not top 20 school, and am dealing with similar worries. Leaving aside the statistical atrocity that is the U.S. News Rankings (and hoo boy, don't get me started) one thing I would say is that, as far as I can tell is that the school's reputation is only as important as who you're working with, who's writing your letters of recommendation and will vouch for you on the job market. Of course the two are seriously related (that's why the PGR has been so successful in philosophy, in my opinion anyway) but as long as your self-esteem doesn't depend on the ability to immediately get a TT position at an Ivy (or Ivy-like) school, being in the top 50 is already pretty good. And the thing about a terrible job market is that everyone is feeling it.
All that being said, I spent about a month or so thinking about all the ways I would fix up my application to do better next time, to the point that I didn't actually know how to feel when I was actually admitted somewhere. It sounds crazy (because it is) but that desire to do better is part of what makes me a good academic--and my ability to procrastinate is what made me a bad applicant, but I digress--and I'm beginning to see why my professors think it would be a mistake to pass up a good offer because, what? I want to impress people even more at dinner parties? I mean, I certainly feel the temptation, but I think my reasons are...not so good.
Maybe a calmer head (than mine) is needed.