Limited use means you need to get more from other roster spots, at some inevitable point it's not worth it. And I never considered him a locker room leader. Solid guy but not a star.
General concern, only slight decline so far but I think history shows it generally happens fast.
IIRC this is not the first time recently the Pats have let Faulk go to free agency, I suspect they are suspicious of his declining but keep bringing him back at low cost and end up being surprised. But if there's a chance they could use his roster spot to hold on to some promising young draftee or UDFA who could be here for a few years I think they'll take it. At this point he's short term no matter what.
Look at Vrabel last year: in decline, still expensive, so he was gone. Faulk's relatively low cost may save him again this year.