What can we learn from TPTR other than (i) fictional truths about the film-world (Dr Jacoby is cranky), (ii) about Lynch's worldview (infidelity is trouble), or (iii) about mainstream moving image media (most spectators don't enjoy narratives that don't focus largely on character's solving problems)?
It's a good question - one I wouldn't venture in until we can watch the show as a whole: I feel tryin' to figure out Mulholland Drive, being only 50 minutes into the movie, would be a pointless task and would somewhat belittle the movie.
Is Diane complicit with DoppelCooper, and/or is the allusion a red herring?
I'll riff off your question, Richard. I take (i) being puzzled as the key viewer engagement motor of Lynch's work and (ii) much of the pleasure that this evokes (outside aesthetic experiences we don't usually enjoy being so befuddled) stems from being made aware of the implications of the (cognitive) processes involved. So, realising and appreciating the many possibilities raised by Diane's response to DarkDale's message foregrounds a number of things, i.e. what we want her to be, how Lynch toys with us, how our experiences are shaped by expectations, how our views change as new information becomes available, what the (often unexplored) capacities of film are, how long we can maintain an interest in unanswered questions, where our worldview or philosophy of life might be flawed...