Sammy doesn't need a mentor, he just needs to stay healthy.
Boldin's production in the Bills running offense would drop significantly from last season. He's not getting 100 targets here. There may be better things to do with the cap space than sign him to take targets away from Watkins, Jones, Clay, McCoy etc... Couple that with his age and dropping ypc and it really doesn't make it a no brainer like most seem to think. He's not signing for the vet minimum.
He would already be signed if he was such a hot commodity and mentor/leader.