Definitely worth going to and spending a chunk of time there.
We had been before and were just wanting to see the 'Zodiac' ceiling again, having heard it had been cleaned up. This was, unfortunately, wrong info and it was still overall black as previously!
However, this didn't stop us looking at everything else yet again since you have to pass most of it to get to the roof area anyway.
See photos at http://www.flickr.com/photos/elaref/collections/72157633385714775/