A lot of fun can be had, from a writing viewpoint, in denying your characters their wishes for as long as possible in the story. You then see how they overcome the obstacles in their way (assuming they do, of course).
If you want to unleash even more chaos, then let some of the wishes of your characters come true. Getting what you want isn't all that it's cracked up to be at times. How would your characters react if what they wished for wasn't as good as they thought it would be? (They'd probably be more careful what they put on their wish list another time though!).