These self adhesive jewels look great as sconces on the walls or light fixtures on the ceiling of your theater. Put the larger ones towards the opening, and have them get smaller as they get closer to the stage. This helps with the perspective your eyes will see, and helps make the illusion of the movie theater even more dramatic.
Also, they look great on the marquee.
Glow in the dark paint looks great on the above light fixtures and sconces and also looks cool as lighting for the floor. Again, put large globs towards the opening and have them get smaller by the stage. Shine a bright light on them for a few seconds before the “show”.
Find some images that hold a special meaning for your audience such as wedding or baby pics, favorite vacation spots etc. A quick google search will dig up some cool royalty free frames to drop them in, then print them out and mount them on the walls of your theater.