It could get even better if you already planned on carrying an Enchanter's Ring and can throw an Aysra's Touch on it for 1 more mana to make it a little safer. 2 Spellbook points, 5 mana, plus 1 added life to the Priestess for a creature that might be able to survive longer than the normal crystal/flower if someone actually targets it. Add a Guardian Angel or a wall and they're basically untouchable and you can stack them in 1 zone.