There's certainly something to be said for being the first one to come out with a big idea, but be careful. Jumping on a hot topic too quickly, before all the variables really have time to reveal themselves, might be devastating to the book's success.
Take our current economic crisis. Authors and publishers are eager to produce the book that will shed great insight into the situation. But who really knows what will happen? Anything can, and that's the risk for stating one's case too soon. Being first isn't what it's always about. But being accurate and insightful usually works every time.