IMO, one should decide whether the spell is to be designed for casting-specced casters (Max Int/Cha with all level-ups and corresponding feats) or for melee-specced casters (High base Str, mediocre Int).
I lean towards the second. What casting-specced caster would go in melee in mid-end game? With all the SLA's we have it's no longer necessary (although could be done semi-effectively).
However extra SP cost could ruin it for melee-specced casters. DP clickies could be the better alternative.
+6 Morale or Exceptional (thats +4 over Rage or +3 over Endgame gear, right?) to Str and to Con could be a bit OP.
As for the advantage of spellbook-casting over scroll casting: A decent duration would be already an advantage.
Infant