The question about Sanders is how many snaps will he get with the current makeup of the secondary. Just for grins, say there are 65 defensive snaps X 4.5 DBs on the field on any given play. That means there are 293 available snaps.
Minus 130 for Bodden and McCourty
Minus 100 for Chung and Meriweather
That leaves about 63 snaps left. Butler and Dowling would need half of those just for development (why keep Butler if he doesn't play? why draft Dowling at #33 if he doesn't play?).
Now there are just a little over 30 snaps left for Sanders. Even if he takes all of them...shutting out Arrington, Page, Sergio and the rest...is that the best use of those cap dollars? Pending injuries and surprise cuts (Meriweather/Butler), that is a legit question.
As for leadership, the 2011 team is completely different from last year. Outside of Wilfork and an emerging leader in Mayo, there wasn't much else for locker room leaders last year. Wilfork, Mayo (established), TWarren, Bodden, an emerging Chung and a surprise leader in McCourty are all patrolling the locker room this year. The only newcomers are Dowling (team captain, respected on and off the field), Stroud (strong locker room guy) and potential FA edge rushers (bet only Boy Scouts will be considered). This defense really isn't in transition anymore and doesn't need a babysitter.
Sanders did set the defense a lot last year, but if Chung and Mayo can't get the defense set correctly this year they should be replaced. Sanders is a limited player that makes up for it with effort and smarts. That just may not be enough to fend off the talent behind him. At $3M+ and a part-time role, his spot on the roster is and should be in question.