I wonder this occasionally too, with one additional consideration: does the kind of camera you look through change how you experience it?
With SLRs and rangefinder-types, you look through the camera, with it between you and the world, possibly removing you from the experience. With TLRs and cameras with waist-level viewfinders, I feel like it's not so removed... that there isn't a screen up, and I can compose, focus, and shoot without losing engagement.

Thoughts?