We just got off the 8 day Valiant cruise as well. The lines were very long, and while I didn't see anyone turned away, every seat in the house was full for shows we saw in the Red Room and Manor. I assume there were people that weren't able to get in.
We were lucky to be Rockstars this cruise, and were told by our agent to arrive 35 minutes before show time (5-10 minutes for Ship Show), and there would be a priority line. That line was let in first, so we had first choice of seats. The big line is let in immediately after priority.
We showed up just as the normal line was entering the Manor for one show (which had a huge line), went to the front to ask if there was somewhere we were supposed to go, and were "cut" into the line and guided into the venue by staff. We ended up way off to the side but got to see the show.
As far as I know, there were no reserved seats for RS's. For Duel Reality, the RS line went in first, then the big line, then they let people into the upper section when all of the lower section had filled.
Honestly, I would not want to have to wait in line and would likely just skip the shows if we weren't RS. Some of the lines started forming 45 minutes or more ahead of the show, and especially for The Manor, having to manage the line through the Casino must be a pain.