Thanks for your replies! The spell becomes rather powerful if it substitutes the "prepare herbs", since this frees up lots of dev. points for an animist, as he doesn't need this skill with this spell. On the other hand, the spell is not very powerful otherwise, since there are very few herbs (there are some, especially if you include poisons) which is described as taking time to be effective. It's not "repairs bone in 1-3 days"; it's "repairs bone". Also, the herb will last much SHORTER than otherwise, as a herb USUALLY lasts longer than the effect described in the spell.
Other comments are more than welcome. Another question: Do you count plants that work as poisons as herbs? If so, this spell DOES have some value even if "prepare herbs" or "prepare poison" has to be used, since some poisons are slow in their effect.