Sure, go for it. Even if it never gets off the ground you'll learn an enormous amount from writing it. These days it's possible to publish on the Net very cheaply and, who knows how successful that might be? It's potentially an enormous market out there and you only need to sell to a fraction of 1% to make a nice profit for your labours.
I'm writing a book as well and I've been wondering the same thing. But I'm thinking hey, you only live once, take a chance and see where it takes you! You never know, it could lead to something really great!