I agree with whats been said, and thats why Im not into them much.
firstly, I think its always better to investigate and tear the game apart by yourself first, then move on to a stronger player and ask what he thinks of the lines, and then move on to a computer if theres still knowledge to be gained.
usually I dont even go that far though. when Im looking at game later (REST is important to me) I try to focus on the points I believe to be key, and points where I felt the most stressed/confused.
secondly, I agree with the OPs last point.. the part where its essentially the winner bragging and the loser being a goody-goody, dispite possibly only a 12 point rating difference.
unfortunatly its the same in books a lot. they will praise the winner of a game the whole way through, and the loser will be questioned every step of the way... despite the game being equal til move 23. its like a hollywood script- good guy, bad guy, moral (avoid giving up the bishop pair for nothing blah blah blah)
Post mortems are generally worth the time for me, either for receivng good info or giving something of worth.
One rare type of post mortem I experienced at a local chess club was with one guy I beat fairly handily. He kept saying What would you do if I did this. I told him that I didn't want to play a whole other game. He seemed intent on somehow turning that loss into a win.
More common and more distressing is when during the post mortem it becomes very clear that you saw much more than your opponent, even when you've lost. Especially when I've lost I say to myself How can you lose to this idiot? a la Nimzovich.
I've got to be realistic though and acknowledge that I must be a dumbass in turn.
Such a post mortem can really be a psychic drain.