The only constant variable in every single terrorist attacks, is the potential to produce mass casualties. People are way over-playing the, "symbolism", aspect.
Would bombing a movie theater create more casualties? Maybe. Maybe not. The biggest thing to think about: how are you going to get the bomb positioned and where are you going to place it?
The Bean Town Bomber used pressure cookers to camoflauge his devices. A pressure cooker, sitting in the aisle of a picture show just might draw some attention. A pressure cooker, in a garbage can, on the sidewalk? It would go completely without notice.
BTW, pressure cooker bombs are very popuar in the ME.