Good post and I'll play devil's advocate on this point.
Haggans was an underrated FA acquisition, and an important part of our superbowl run in 08. I appreciate his contribution to our team. But he was in decline even then, and is certainly running on fumes now. He's what, 35 or 36?
Because roster spots are so valuable in the NFL, we can't afford to waste one on him, especially at a fairly critical position (I believe a team needs a 3-4 OLB to pressure the QB). Better to bring in a prospect with the opportunity to develop into a star, while providing probably more production and big plays than we would likely get from Clark. Also, I'm confident that either Dwash, Schofield or Acho will emerge as a defensive leader.
Again, good topic, thanks for putting it together.