Gary,
This is sounding very interesting. It sounds like one of those games which is a great concept but I'm not sure how you'd implement it to make it fun. The idea of a civilisation discovered through past messages is great.
I'm interested in any mechanics you've got.
My doubt at the moment is whether I'd want to spend lots of time writing in a game session. Unless, and I've just thought of this, it's a specifically play-by-IM or play-by-email game, and then I'd be quite happy to write.
Good luck! As for whether this is better than All the World's a Stage, I think ATWAS is more implementable but this is a more interesting concept.
Graham