I think it's funny also when people say the books are a "San Fancisco" thing, as when I went down to see the show, it was my first ever time in San Francisco (my sister's too).
And she seemed to get the plot of the show just fine, even though she's reading the books now (she started a week ago, and just finished the second book).
So there must be some sort of univeralsity to the characters that attracts us to them.
I do agree, though, that the books did get a little weaker as they progressed. But even reading Maryanne (which I did on the plane ride to and from SF), which had a lot of hokey plot points and a few overgeneralized characters that didn't have all the nuances of the prior books, it still was like revisiting an old friend.
Xanadu! Can't cry on cue!