I've come to believe that "serious listening" should be seen as an oxymoron. That's probably not exactly the right word, but why is what is supposed to be a hobby and for pleasure ever "serious"?
Which is another way of saying I agree with you, although possibly one symptom removed. It's when you stop listening for enjoyment, which doesn't necessarily mean listening while doing something else - you can listen for enjoyment in a dedicated way, that you start analyzing the sound. The activity you're doing has changed its nature, quite possibly without you overtly deciding to do so. That's not the sole reason a person gets the upgrade itch, but it certainly is a leading reason.
Which is another way of saying I agree with you, although possibly one symptom removed. It's when you stop listening for enjoyment, which doesn't necessarily mean listening while doing something else - you can listen for enjoyment in a dedicated way, that you start analyzing the sound. The activity you're doing has changed its nature, quite possibly without you overtly deciding to do so. That's not the sole reason a person gets the upgrade itch, but it certainly is a leading reason.