Re: Harry Potter
I've been involved in the movie business and one of the big problems with large productions is the fantastic waste of time on set. Small production companies that don't have unlimited budgets seem to be able to get far more screen time as a percentage of working hours. If the goal was to produce movies that were closer to the books, there is no reason why it couldn't have been done before Harry, Ron and Hermione were middle aged.
In the case of the Harry Potter stories, broad appeal and hardcore fans might yield fairly similar numbers. There are some things that I wouldn't miss if they were cut, but I would have liked to have seen more of the adventures of Fred and George. And I could go on for pages about stuff in the movies that was made up or extrapolated to extend action scenes (Goblet of Fire).
I'm just frustrated when the movie rights for a book go to a film that is only very loosely based on the text when what I really wanted to see was was a more literal adaptation. It's not like they couldn't have taken the broad outline from a book and written a good screenplay and titled it something else with different character names and set in a different location.