Readers (at least, this reader) will put up with a lot of improbability in reading fiction (as they will in watching movies and plays). Someone (Ben Bova?) once said you’re allowed one coincidence in a plot, but that’s certainly not a rule that Shakespeare or Dickens followed. All plots have some degree of improbability, because life doesn’t have a plot. Psychic spy thrillers like Summit and uncategorizable novels like 1Q84 just have a different kind of improbability from that of novels that purport to be realistic and don’t rely on psychic powers or parallel universes (or hobbits or warp drives).
But when you move outside the everyday world, you need to make an extra effort to ensure that your improbabilities are consistent and, at least at some level, believable. That has a lot to do with the texture you give to the characters and their world. Murakami has 900 pages to play with, so he can put in a huge amount of texture. But you also have to be sure that your world is pretty darn interesting if you’re going to ask readers to spend that much time in it.