How busy are they on Sunday nights? If I show up about 30 minutes before showtime will I still get a good spot to see the show?

They might not be too busy but it depends mainly on what your going to see

They were really busy yesterday, but I assume it was because of avengers endgame opening night. On a big opening night like that you should show up pretty early, I spent over an hour from the 50 freeway exit on Bradshaw to the paying booth.

I dont think they are that busy anymore so you should be fine