I haven't had a ton of time with the Ether and I haven't listened to them back to back so take this with a grain of salt: I think imaging is about the same and I think the soundstage on the open is bigger (because it's open!).
That said, the soundstage on the C is probably the biggest soundstage I've heard on a closed can. Dan says that the soundstage on the closed one is actually bigger, but it's hard to tell unless you're in a silent room. He says that in a loud room, the isolation cues your brain that you're listening to a closed can and so you perceive it to be smaller than it actually is. Without that external cue, you can tell that the soundstage is bigger. Note: you still won't have the "air" of an open can either way. That's part of the tradeoff of going closed tho.
Again, they're very close in many ways. Much closer than you might think from all the impressions bouncing around.