I've read the keys to ET messages one, and I've read around a little bit about it. It seems the two views of it are that it's a legitimate attempt to decode an alien signal which the NSA has disclosed to the public quietly in order to lay the ground for ultimate discloser of UFOs. The second view is that it was a training exercise to see if they could decode a legitimate ET signal if one were ever to occur.
Regardless of it's origin, I think it's an interesting read in it's own right, and I think the method and logic to it could be useful in decoding crop circles. My first attempts to decode crop circles were based on this very paper in fact. So I think there is value in it for someone who is mathematically inclined, or even linguistically inclined, but I think it's fairly useless in trying to understand UFO's and ET intelligence. This is because it doesn't give any other information about the circumstances surrounding the signal except that it was a radio transmission from outer space.