Mike,
So the real question is -have you managed to get something working in AIR using the HTML/Javascript interface? I’ve had a quick go myself with main stream Flash authoring and it seems to work pretty well – if a little rough around the edges. But what you seem to be hinting at is that you managed to make something which looked pretty nice using a free text editor and the web skills you already have. Regardless of the actual technical issues between WPF, silverlight etc this seems to be the key advantage that you’re talking about.