The Skill "Path of the Mage" gives 50% spell *damage* bonus.
I noticed once I acquired this skill that the tooltip of the "Heal" spell shows 12HP instead of the normal 8HP once this skill is gained, but when the spell is cast, it is still 8HP.
There is something wrong here: either the tooltip or the spell itself if the word "damage" was not the one intended and all spells were expected to benefit from this skill.