Honestly, I have no idea why there are G-Healing Grimoires.
Originally I had assumed that Shaman would get a bonus from them (maybe cast speed from Grimoires instead of Staves) but that wasn't true. It's really mystifying as to why they're even in the game. I think a Cleric or Shaman would be better off with a Lv10 white Mace/Staff respectively than any of the healing books, assuming they aren't trying to deal damage.
Based on the this
thread Sage is going to have a Hammer bonus, so the books STILL won't have any decent use. Really is a shame, I think.