Amazing work on those covers. The design is just brilliant.

Just some small things: The size and position of the movie title changes slightly between Empire and Jedi. You might want to change that although I'm pretty sure you wouldn't even see the difference when printed.
And the actor names are a little hard to read with those white lines, but that's no big deal either.

And since you mentioned adding Vader: You could replace Obi-Wan with Leia, Leia with Vader and Chewie with the Emperor. That way Vader wouldn't be the only villain, but you'd loose some of the good characters, so I wouldn't actually change it. But I thought I'd mention it anyway.