Maybe I'm being too paranoid. I'm not sure. I just have a gut feeling that this is too ambitious at this time.
Now, if we were to go to them and tell them that Poly's server is apparently down, and thus they are operating sans forums, it couldn't hurt our relations.
And if we tell them that we want them to know that if either Poly or GC gets nasty with them, we're going to back them up 150%, and ask them for the same in return, I can't see that backfiring either.
My point is, I feel like a formal alliance is a scary thing at this point. The thought of it makes me feel a bit exposed, like we're putting a bullseye on our foreheads for both Poly and GC to shoot at. I just figure that word of a formal alliance will get around and we'd be foolish to sign up for one without considering the consequences of such action very carefully.
Having said all of that, I fully admit that it is quite possible that you are 100% right and a document like this is the best way to go, and if the rest of the citizenry agrees, then I'll just have to come to terms with my paranoia.