Yeah going to the theatre whilst high on MXE might not be the best of ideas. It would almost have to be very low doses unless you want to be carted out of the auditorium by the ushers who found you dribbling on the person in front of you raving manically about finding the elixir of eternal life.
I've watched a couple of movies with friends whilst high on ketamine, and to be honest it was a complete waste of time because I couldn't comprehend anything meaningful. Although I know there are some on here who will disagree about this, notably psood0nym who claims to have had some pretty deep experiences with movies + dissociatives. Try it, and see if you like it. My only advice would be to watch something uplifting. Dissociatives and psychedelics have a tendency to make you more subconciously susceptible to perceptual stimuli, so things absorbed whilst high can really get stuck in your head.