How Do You Know a Story is Worthy of a Podcast Series?

I wish I had a nickel for every time someone says, "I think that story would make a great podcast series." In my head I usually think, "Nope. Wouldn't work." But why? How do you know you have a story worthy of a podcast series? Emily Guerin of Southern California’s KPCC has a few answers. She produced a five-and-a-half-minute feature and turned it into a 9-part series called "California City: The Dark Side of the American Dream."