Personally, I believe Firefly Queen was enough powerful as it was before (even with 7
cost) and the reason it is not very commonly played is because it fits into certain combo decks; it is not just an Air creature you will put anywhere, is it? Because of that, I don't think the less cost will make it more commonly used, but I think it may helps, so lets make her a 6
creature! If it doesn't works, it can be fixed later.
As for the artwork,
why don't we have two seperate artworks, one for the uprgaded and one for the not-upgraded version? There are so many creatures which have distinct artworks between their upped-unupped versions (Otyughs, Armagios, Shriekers etc.), so why not to add this to every kind of creature card too?