yes, if we were to find some other worlds that were the same as the earth, it would make a huge difference in all of the things that we know know and in all of the things that we think this world is as of right now in this country.
Yes, I do think that finding Earth twins would fundamentally change our philosophy and values, because we would have to question our very existence. Everything that we know and believe has been predicated on the fact that we are the only and most intelligent creatures in the universe. Earth twins would shatter our beliefs.
When I hear the term Earth twins, I am assuming a world that is much like our own that is also inhabited by humans. I believe if we were to find something like this it would more than likely change our philosophies and values. Of course it is hard to tell what this other group of hominid creatures could tell us about their experiences in the Universe and that information would make a lot of difference.
No, I don't personally think that finding twins to Earth would change our values and philosophies. The reason is because even if we ever find a planet that we feel has the capacity to sustain life, it would be too far away for us to determine for sure that it has life, or what type of life it would have on it. So while it would be an interesting discovery, it wouldn't be something that would change people's opinions about life on our own planet.
Just because there are other worlds and possibly ones with other creatures capable of self-consciousness with their own societies and values should not fundamentally change the way we are. Society was built from years and years of understanding ourselves as human beings, and as human beings this is, for better or worse, the way we are.