At 29 he fits the Bills mold of older and talent deficient running backs (save for McCoy).
You are absolutely right it hasn't worked yet and it reeks of bringing in their own guys just because of that in and of itself. KB cannot separate, Star was atrocious if you look at his numbers analytically, Tolbert was the joke of the team last year, and guys like Kealin Clay simply steal roster spots.
I may be in the minority but I am not impressed with the talent building on this roster esp in free agency.