As far as I know, the only thing that Spells benefit from are:
- Every % Damage (Including of course the +% Total damage)
- Intelligence (Only Elemental Damage, the DoT Variants and (here called) Magical Damage)
- In some cases also absolute Damage increases (like +30 Cold Damage for example) but only by very few skills, and also only if the bonus is not on a weapon or shield (here I think the Bonespear is the only spell that uses this mechanic)
Strengh does not work on physical damage dealt by spells (This is kinda dumb in normal TQ IT, because a Melee/Caster Hybrid with the Dream Mastery isn't so awesome as it may sound at first...)
The problem with the Staff Attack is, that the way Violos did it, he can't give it the effect from the Bonespear, thus only % Damage increase gives you more damage. Also the attack should be a spell (not sure about this) so, if anything, it would be casting speed (but again, i'm not sure here).