Sorry, I didn't notice your card since you linked it. xD
My idea is quite similar but Echo doesn't recast the last spell (that could be OP in my opinion), it only add to your hand a copy of it.^^
The part of adding to the hand was my first idea and is part of the poll that is there, and the mechanic of resonance is exactly as if you had added to your hand and played it right after adding it to your hand (that includes paying the card spell cost). But anyway, you don't have to be sorry, your card is better worded than mine and I'm supporting your card, I want it to win. Great mind think alike.