I've never been an avid play reader, but for different reasons. No, it's not because I break down every play I read as if I were working on it, but because plays (to me) are not written to be read, but are meant to be performed or interpreted by actors. They were written to be watched, brought to life onstage. And, as I am not a director, I don't picture sets, lights, staging, costumes, actors when I read a play. It's different with a work of fiction, somehow I can picture everything when I read a good book. But not with a play. I guess part of me is waiting for a director and designer's visions.
But, like Matt, when I'm working, I read the play for paperwork in pre-production, and then wait for the read-through to take additional notes and really get a sense of story. (Thanks for feeling so free to admit that, Matt. It makes it easier for me to get in line there with you!)
As for watching plays, my favorite thing is to go the theatre and NOT notice the SM's work. I want the play and the production to be so good that I am entirely entranced by the story and the emotions behind it, for two hours or so. My best evenings in the theatre have been those, when I forget for a while that I know all about the backstage workings and am truly an audience member. After all, that's how I want you to feel when you come to a show I'm working on. I don't want the audience noticing my work at all!! I want them to be one with the transcendent power of the whole theatrical experience.