R&S: If SETI were to ever find a signal, do you think that will trigger the calling for world government?

Not necessarily. Man has had many opportunities to form a world government in the past, and it has never come close to happening. I see no reason why people would suddenly decide to do this, just because they know that "we are not alone". More likely, each nation would vie with each other to make friends with the extra-terrestrials, trying to be one up on the other nations.