I didn't have a problem with the use of "The Arena" march in ROTS during Vader's entrance into the Jedi Temple. It didn't strike me, during either of the times I've seen the film, as out of place. Would it have been nice for Williams/Burtt/Lucas to have written/edited/used a new piece of music? Yes. Does the use of "The Arena" ruin the scene for me? No. It's still a powerful scene. Just my two cents on that one.