If Iridescence is just the normal day/weather bonus it won't all be roses and sunshine, you will get a damage penalty when using a spell weak against the element of that day or weather. If you are SCH or /SCH you can get the weather bonus or at least prevent the penalty, but the day can make it a wash gain-wise. (And if you are /SCH, you won't have Thunderstorm, Voidstorm, or Aurorastorm so you would get a constant penalty for Water, Light, and Dark on those respective days. But no one really cares about Water nukes anyway...) If you don't have storm spells available, I imagine that that could be quite inconvenient.