Headley's back stuff is of concern. Without his HitFx data available, none of really know whether or not his currently *low* BABIP is good indication of his true talent or not. He might be hitting as many line drives as normal but if his back is f***ed, he might not be able to hit them as hard. That obviously has an effect on his underlying BABIP skill.
There's also opportunity cost associated with going after a risky asset like Headley. Sure he comes cheap but if he truly is a hurt sack of poop that falls apart on turf in mid August, you're not going to be able to react in time to get a Zobrist or equivalent (for a piece or two more obviously).
But, to argue with myself, if we are to believe Headley's back is f***ed, why hasn't it shown up in his defensive profile yet? I suppose it could be the specific location in his back that only really hurts during the torque of a swing and not in bending down, to field a ball. Tough to say without seeing his medicals/having a professional interpret them.
(And because someone will surely say it/think it - yes this is a small sample size for any fielding data but keep in mind that any ball in play offensive metrics need as much time to stabilize as UZR does.)