The question is whether Peters is overpaid period (meaning no one is worth that money) or overpaid based on his expected performance and, ancillary to that, did the Bills come out winners or losers in the trade.
Assuming for a moment that ProFootballFocus.com has accurate rankings (I'm making no judgment either way), then Philly did overpay for him simply because he was expected to be much better. Nevertheless, he still ranked way ahead of any of the Bills linemen (Hangartner was the Bills highest ranked lineman as the 27th best center).
Since Levitre and Wood were rookies, I think it's unfair to judge this trade just yet. Now, I wouldn't be surprised if the Bills get hosed in the end, but I'm still reserving judgment until I see if Levitre and Wood can pick it up a notch.
Incidentally I find it interesting that our "big free agent" signing on offense so far has been Cornell Green who, according to these rankings, isn't much better than what we have (and note that Michael Oher ranked one behind Peters at 19).