well since it's an aether card you can easyly quint it result to an unkillable copymachine for dim shields for example, OP for aether IMO, also the test say"...of the target card", i'd will say permanent 'cause also creatures are cards.
I see your points... It's aether simple because it feels like aether... like fractal and duality... in its function.
And it can target all the cards, including permanents, spells and creatures as long as they are in hand.
To make it less powerful, I'm thinking about making it more vulnerable as its life decrease every time you use the "copy" skill. Therefore, even if it was immaterial, it would die soon. And to use blessing / heal /... to keep it alive, you should not make it immaterial.
How about that?