I think what you are asking for is a measure of the Information 'density' of a posting. This is a hard thing to quantify, since what is 'information' one One is 'old news' to an Other; it depends on each persons 'context'.

Well, but then with a strong accent on fun. In this sense Roy Johnson's reply is very much in line with it... In fact I think that what I'm asking very much boils down to to a measure of wit, although of course wit itself is not something you can easily measure, nor with difficulty, FWIM. Yet, I'd still be curious...