Sanders and Lewis are lock Hall of Famers and among the best to ever play their positions, so I can assume you mean overrated based on their skills TODAY?
If that's the case, i would content that Sanders isn't overrated...he was a part-time nickel back for an OK, not great, Ravens defense and is retiring because he's washed up. And while Ray Ray is no longer the most dominant defensive player in the game, he's still among the best at his position IF healthy.
Sapp is also a potential Hall of Famer who was CLEARLY the best defensive tackle in the league for much of his career [but he's been overpaid by the Raiders for sure, surprise surprise].
Of the younger players...
Urlacher is a true stud. Just listen to his teammates talk about him, they universally contend he's the glue that makes the Bears defense unstoppable.
Peppers is a bit overrated in that he gets by on physical talent but hasn't honed his craft to meet lofty expectations, but he's still among the league's top DEs.
Champ Bailey probably wasn't worth what Denver gave up for him, but he remains one of the few true man-to-man cover corners in the NFL.
Dan Morgan can't win this, because I'm not sure many people even think of him as an elite defender, do they? I certainly don't.That leaves Kearse, Arrington and Roy Williams.
While Roy Williams absolutely isn't the do-everything impact safety people thought he would be out of Oklahoma, he is an excellent in the box safety and really found his role again in the Dallas defense this year. Plus, I'm not sure anyone really considers him the best at his position [Ed Reed, Brian Dawkins, etc...], so I can't vote for him.
That leaves Kearse and Arrington...tough choice.
In terms of pay, both are HIGHLY overpaid. Kearse got HUGE money from the Birds [biggest DE contract ever at the time] and has back to back sub-8 sack seasons. The Eagles brought him in to gobble up double teams and be a force, yet not only has he been ineffective when doubled, offenses have actually STOPPED doubling him and yet he's still erratic.
But I have to give the slight nod to Arrington. How the guy made so many Pro Bowls is baffling. When Joe Gibbs, Gregg Williams AND Marvin Lewis all basically say you're undisciplined and hurting the team more than helping, I can't see how anyone can argue that Arrington isn't worth the hype or the $$$$.