honestly... the quickest way to become relevant is to have a QB. by in large, look at teams that have sustained success (relative, not necessarily superbowls) in the last 6-7 years. San Diego, Denver (since manning), Indianapolis, New England, Baltimore, Pittsburgh, Green Bay, New Orleans, Atlanta, NYG... they all have stability at QB. not necessarily world beaters.
you also have SF who has had sustained success by getting everything solved except QB, but thats a much more difficult formula to follow... need to completely nail everything else. offensive line, running backs, tight ends, entire defense... you have a lot of teams that are well built but their lack of qb holds them back. most recently the bengals and bills. the vikings in the pre-favre days. the chiefs with matt cassel. look at the cards without palmer