Hm, I can't help but think your line of thinking is only factoring (or perhaps factoring in too much) stats.
Peppers is a dynamic player that would surely command double teams in some key situations. Those double teams open things up for other players.
Peppers has also been through adversity, and has yet to fail in over coming it. He's been on some under performing teams, had some tough seasons, etc. and he'd fit in so well as a leader type figure that Charles and Al claimed we needed. If Peppers also alludes a type of quiet confidence when he plays, that too would surely help boost our D in light of the constant failings near the end of the games.
That said, he's 29. Ted will not over pay for a free agent DE whose long term success is not highly assured, I feel, especially after KGB became a shell of himself in a matter of months.
I'm pretty sure money spent on Peppers could be better spent (and a lot less spent) on going out and getting talent that is familiar with the 3-4, especially some of the older vets that are on their last legs, but crafty enough to use their experience to their advantage while at the same time helping fellow players new to a 3-4 transition to that scheme and style of play.
The NFL: Where Greg Jennings Happens.