Should have said borderline #8-#5 seed. Out of playoffs or wild card.
The QB position must be the fundamental building block. If you go get a guy who is 30 or older & you just make it to the playoffs it's unlikely you can sustain this level over 5 seasons. See Arizona (Warner), Bills (Bledsoe), Favre (Minnesota), Favre (Jets), Montana (Chiefs), Palmer (Oakland).
With a rookie QB you get 5-8 seasons before your guy turns 30.
With a team like the 49ers or Denver who made the playoffs in 2011 inspite of their QBs Smith / Tebow, then it makes sense to go get Peyton Manning.
The Bills haven't proven they can get close to the playoffs with talent around a mediocre QB, so it doesn't make much sense to add a veteran QB. By the time the rest of the team would be built the QB would be well past their prime.