I've had an idea for a mod for a long time that would add lots and lots of low detail societies to give players small passive bonuses and add to the complexity of the game. Things like the Merchants Guild, Troubadors, and Copyists, all the way down to such informal groups as Polite Society, Young Blades and the Debauchers club. Every one of the above societies would add little more than opinion bonuses for fellow members, maybe some inside assistance (eg free favours with fellow members, general opinion or prestige boosts etc) and maybe access to small loans or some other intangible aid.
Not every society should be geared towards destroying the world or saving it !