I thought he was great with Neil and/or Crazy Horse - esp. After the Gold Rush and Tonight's the Night - but also on the most recent Neil/Crazy Horse album Colorado.
Never been a big fan of the Boss so don't have much of an opinion on his contributions, but ultimately don;t think he would have been the right fit with the Stones.
Might have been nice for a track or two on Black and Blue the same way we heard Harvey Mandel and Wayne Perkins, but can't imagine him on Some Girls or anything beyond.
That said, he could have contributed nicely in a live setting to help buffer and cover for Ronnie...sort of hidden in the wings...
_____________________________________________________________Rip this joint, gonna save your soul, round and round and round we go......