Yea, I agree with others that the "out of resources" part is the worst of reasons to go elsewhere, but we still should. As slim a chance as it is, a mass extinction is a much better reason that resource depletion.
Humans need to learn their lesson and take care of Earth instead of trying to trash and exploit everything they can land on. But hey, greed does not have the ability to stop itself and use common sense.
No, it would first of all cost a ton of money and probably send the world into bankruptcy. Second of all there would be too much fierce competition for which country would get the honor of colonizing first and since Earth is not a perfectly peaceful place, this won't be happening anytime soon, if ever.