This is not a proposal, but a commentary on the idea that (hopefully) might lead to some other brainstorming.
There's a set of ideas in the philosophy developed by Paul Grice that relates directly to the assumptions made in order ability to have a rational conversation. I should emphasize these are not rules; flouting the maxims is entirely possible, and in the theory is what gives rise to sarcasm, irony, and many other forms of speech. Briefly, they go like this1:
Cooperative principle - Contribute what is required by the accepted purpose of the conversation.
Maxim of Quality - Make your contribution true; so do not convey what you believe false or unjustified.
Maxim of Quantity - Be as informative as required. Do not be more informative than is required.
Maxim of Relation - Be relevant.
Maxim of Manner - Be perspicuous; so avoid obscurity and ambiguity, and strive for brevity and order.
I think these are interesting to think about, because the site is inherently conversational. One person asks, other people answer. So, do we manage to do these things?
On the whole, I think so, but I'd like to highlight the idea of relevance, where I think we do slip a little.
It's important to remember that we are answering questions, and an answer that is not relevant to the question isn't a very good answer. Information can be true – even excellent – without being relevant, and sometimes is actually quite wrong in the context of the question2.
1 Anyone particularly intrigued can the good overview at Wikipedia, and more thorough treatments in the Stanford Encyclopedia of Philosophy entries on implicature and pragmatics.
2Just for emphasis, such answers do exist on the site (at least in my opinion), but I don't think it's relevant here to point fingers specifically. I've already done my part and voted them down. :)