“In all the UFO movies there is an advanced civilization that seeks out lesser advanced planets. That all supposes that these advanced civilizations came first. What if we are the first?”
Good point! Not nearly as much fun, but good point nonetheless ;-).
The Earth 2 series from a few years back showed humans as the alien invaders.
I personally think finding intelligent life is the last thing we want to find. Better to find a planet populated by edible stupid critters.