An item that increases the cost of your spell by 7 doesn't sound very good to me, shouldn't the user be limited to lower level spells? Because it's not like you have infinite magic points.
@Richman in the MMOs you've played don't you have strong spells that you can use relatively often that, if their damage is multiplied by 7, would be stronger than your long cooldown skills?
granted this isn't great for farming or long raids but it's perfect for short mid bosses