You could entertain yourself with this creative exercise forever, and it would probably never get tiring. In a way, doing so is like a game in itself a game centered on creation and building.
You can use the list of Fun Techniques as a checklist to see if any of them might potentially benefit your game. You can also use this list, as I have here, to experiment with incongruence in order to ignite a few creative sparks and break open your thinking in your game's design.
I don't think the world will ever get to the point where it can't benefit from a little more fun. If you're reading this book, my guess is you already are, or soon will be, upping this planet's smile quotient a very worthwhile endeavor indeed.