1u. Don't think so. Even if u cast spell each turn for full mana u will discount 10 mana on turn 4, 15 mana on turn 5, 21 mana on turn 6, so you can play it on 7th turn in best case. And typical aggro will rush u down before turn 7, especially when u only cast spells. In normal game u will play it on turn 10+ and it will be mostly win more (or do nothing) card. There is reason why galvadon or lyra aren't competitive decks.
2u. It maybe can find place in some weird combo Malygos deck where u can chain spells into face. And you don't want to cast chain lightning on empty board or healing rain with full health to just draw a card. Mana Tide totem or acolyte of pain are better in my view.
4u. No. Just no. Play acolyte of pain instead.