User blog comment:Voads/Aura, The Fairy’s Blessing/@comment-98.207.105.47-20120221214627/@comment-98.207.105.47-20120221214737

So what I would do is make it so you, at max, can have two wards out at a time - lower the cooldown slighly at higher ranks, and placing another ward when you have two out removes the first ward you placed. Also the mana cost shouldn't scale that steeply - Janna's ult costs less than that.