Entertainment Weekly's Mark Harris has several pithy things to say about so-called "niche " audiences in his "Final Cut" column. But this, IMHO, is the money quote:
"Here's a genuinely surprising piece of news about the summer of 2008: In a season expressly designed to appeal to the hordes of kids who are out of school, two of the kiddiest movies so far, Speed Racer and Prince Caspian, have fizzled. And next summer, and for several summers to come, there'll be fewer kids going to the movies, because there'll be fewer kids, period. Apparently (this is the U.S. Census talking), we had a mini-baby boom between about 1981 and 1995. And then came a dip — a substantial dip — in the kid population. In other words, that mammoth group of youngsters that has reliably fueled movie grosses for almost 15 years is now looking less kidlike: They're between 13 and 27. And getting older. And looking for movies that appeal to them. And they're really not going to like being called a niche."