Some Bills' players were definitely worth what other teams got them for--Pat Williams and Antoine Winfield are prime examples of this (and I ,generally, am not a fan of small db's).
Nate Clements is another story- a good player who I wish was still on the team, but not a huge impact player. I believe that he was close, for a while, in making close to Tom Brady money after San Francisco signed him.
New England's philosophy seems to be : get rid of them before their decline and want megabucks. I don't subscribe to this 100%--I think that you have to look at each player on an individual basis.