Yep, I would gladly buy a stronger nice quality dark brown or black leather version of the stock cover. If nice, it would probably make me want to read for purely aesthetic reasons. Similar to how some people feel about beautifully bound books, I suppose.
My only concern would be (and for me it's very important) that it still slides into the dock without having to be removed. I like the dock, and I don't like frequently clipping/unclipping the fastener on the back of the case.
Like Yvan hints at, I'm sure there will be some nice third party covers if the Reader continues to be popular. And people who will spend $350 on a Reader device, probably are a great market for sophisticated looking upscale leather covers also. Anyone listening?.... <hint> <hint> It's a great market opportunity!!!!