Realism stems from three things in an animation or render, in my opinion.
One, the model itself. Try to make your wireframes as realistic as possible, computing power and rendering time considerations notwithstanding. Your model is fine, if a little basic.
Two, materials. If possible, create materials using textures derived from photographs. For example, take a photograph of your loungeroom curtains, adjust the colour in an image editor if necessary, and build a material based on this image. Then you can apply this to the side walls of the theatre (many cinemas I have attended have curtains covering the side walls). Consider carefully the ambient and diffuse settings. In a theatre, the shadows in corners and up in the catwalks will be black, so your ambient setting should be very low.
Three, lighting. Probably the most important consideration, in modelling AND in theatres. There are the overhead stage lights, the follow spot (for live performances), footlights, house lights (for intermission, etc), little blue lights running along the aisle to help you find your seat in the dark, illuminated seat row numbers at the end of each seat row...
Basically, the level of realism you can achieve is limited only by the time you want to spend on your project and the computing power available to you. I have yet to build a model that was too complex for my aging Sempron processor, but I have built models too complex to render this side of the Sun going nova.
