Hard to say without the other changes to monster power in 0.8.0, maybe let us try those first and then adjust attributes as necessary?
Presumably monster HP goes up with each level too, so it requires more spells to finish a fight. A bigger SP pool also increases your time between resting. Regen is the bigger issue with making Will/Con less valuable after a certain point. Simply equipping a 2HP regen ring made me spend less healing spells on my Ranger than before (and instead, I found myself wanting to give him more haste effects).There is a certain mana pool and regen you want, after that every time you get +5 mana for a level up you might be thinking, aw man why did I waste that last point in will
