To put it in terms of Sid Meier -- A culture needs a great project to strive toward. A great common purpose to achieve as a society. The moon landing was such a great project, as was the internet.
I think we as a society benefit to the extent our great projects are positive and beneficial. As humans we can spend our energy and the earth's resources dividing ourselves into infinite tribes constantly battling each other for dominance, or we can work together to build something.
Right now I think we humans are between major projects. The last big one, the internet (and especially the wireless web), we're still digesting. I think having so much information and connection is changing society in a manner similar to the printing press and the industrial revolution -- possibly more. Technology has built us an amazing tool and all we've learned to do with it yet is spy on each other, share kitten pictures and jack off.
So I believe we need big projects to unite us as a society. And I believe humans are instinctively inclined toward exploration and this instinct has served us well thus far. Space seems like the logical place to go.