I think it's a fascinating topic, in fact I wrote a short story on this very topic once. (I'm not a published writer, just thought I'd mention it
I have heard that there are references to 'all the life-bearing orbs of the Cosmos' in certain esoteric Buddhist texts. I haven't ever actually seen a scholarly reference but it is a fascinating idea that such notions were entertained in ancient civlizations.
And I do agree that, for many people, space is indeed 'the final frontier' and something that symbolizes the nearest thing that most modern people understand to immortality. In fact, maybe it is an echo of the ancient idea of heaven being 'up there' or 'out there'.
I would be immensely surprised if anything definite was found through SETI but I have an open mind. It could happen.
But from the viewpoint of traditional philosophy, the manifest or phenomenal realm, whether it's this planet or some other, is only a sliver of a larger reality, which you can't reach via any kind of spacecraft.
//edit// - also check out the Wow signal
He that knows it, knows it not.