Taking inflation into account and the multiple screen cinemas increased capacity, I wouldn't be surprised to find that most modern cinemas aren't doing anything like as well as they were 40-50 years ago before the advent of home video, massive TV screens and High Definition transmission.
Then again, there seem to have been many waves of closures, re-fits and changes of use. A lot of cinemas died in the 60s and went over to concert halls, bingo halls, asian cinema occasionally, arts centres ... When they started closing the big ones in the 80s, there wasn't that much they could do with them. Nowadays you get cinema shows in pubs, cafes and nightclubs and short "festivals" in other places. Some cinemas are only cinemas part of the time.