I recently re-read a story called (I think) "A path less travelled" that was linked off one of the SF pings here that had exactly that as it's main point. Extra-galactics never discovered atomics and advanced rocketry because they discovered the secret to anti-grav when they were at the level of matchlock/flintlock rifles. I really do think that a once the principle of a ZPM module is discovered, it will probably be something that will be incredibly simple and extremely obvious in hindsight. I got nothing to back that up with, but I believe we are meant, by our Creator, to travel to the stars to explore and experience His grandeur and the marvels He has created for us, because if not, mankind as a species will simply not survive. Even if you take the entire solar system into account, there is only a limited supply of resources, and we know that the sun has a limited lifespan.
The road not taken, by Harry Turtledove.
The story itself is a great example of outside the box thinking that once read, shifted my whole perception on the issue and sends me off in a whole new direction of thinking. I had certainly never considered the possibility of a less advanced race coming to earth. We could be surrounded by alien races that simply have no curiosity about us or are afraid of us.