On first glance these enchants seemed really great. Ideally I'd pepper a dangerous mage from afar with a +Magicka Damage bow. And then engage it safely in melee. But in practice I find that if I don't kill the enemy in a reasonably short time, I am dead anyway.
Furthermore the loss in damage compared to straight health damage doesn't seem to be worth it. A 20 base damage sword with +20 Frost damage to Health and Stamina will inflict roughly 40 damage to Health per succesful blow. Whereas the same sword with +20 damage to Magicka, or +20 damage to Stamina, will really only inflict 20 damage to Health per succesful blow.
Do you find these enchants useful? Am I misunderstanding the effects?