Hmmm, I think that if you have some specific "main objective" in mind (let's say, "raising the sanity waterline" or "persuading people to leave religion for rationalism"), that it would probably be more efficient to create a purpose-built forum and then come to this one (and others like it) as recruiting grounds. If you want to, say, make an electric car, you're better off designing from the ground up than trying to retrofit a gas-powered SUV.
In the case of this forum, it already has a long history of being a place where atheists lock horns with boneheaded fundamentalist believers. I think I can pretty much count the theists we've ever had here who do/did not match that mold on one hand: UnkleE, Old Church Guy, Think and Answer, and (maybe) L-Chaim (I haven't read enough of his posts to get a full handle on his theology). The main "intake port" for this forum is the set of "God is Imaginary" YouTube videos. Though putatively addressed to "intelligent, educated Christians," their actual audience consists of people who profess to believe that Yahweh actually does (or did) work miracles--that is, fundamentalists. Just look at the Failbag. Our stable of atheists also tends strongly toward the more confrontational "New" type. Accommodationists just aren't drawn in by "Why Won't God Heal Amputees?" So that's what you get here: New Atheists vs. Fundamentalists.
This forum is not going to attract Christians like Fred Clark or James McGrath or Bishop Spong in significant numbers, because they have already adapted their theology to fit with a godless Universe, and do not try to defend Biblical miracle stories. For them, the question "Why won't God heal amputees?" misses the point entirely, because (their version of) Christianity is more about Big Huggy Bunches of Love or some such
rather than trying to use the Bible as a textbook of science and history.
So, if your intended mission statement involved reaching these more thoughtful/moderate type of Christians, and making sure not to provoke "totally unnecessary emotions," this forum, from its URL alone, would not be an effective tool. If you had something else in mind, like an atheist civil rights activist group, attempting to retrofit this forum into that would likely stir opposition from (at least some of) the "fans" who come here for other reasons. And, you still have that name/URL issue to deal with.
Since the basic setup of this forum and its main marketing tool, the GII Videos, tend to draw in the sort of fact-proof faith-heads least
likely to examine evidence and arguments and re-evaluate their professed beliefs, I'm not sure it's even possible for it to be "effective" at changing minds on any significant scale. It is probably more effective at doing things like creating a community space for non-believers and providing a place where people new to rationalism or already questioning their faith can find a storehouse of atheist arguments and evidence. It can also serve as a "training ground," providing support for unbelievers looking for better arguments to use in their own lives. I have seen quite a few requests like that here, of the "My fundy family members say evolution violates the 2nd Law of Thermodynamics. How would you respond to that?" type.
So, I think if you want to look for a purpose at which this forum can be maximally effective, you have to look to the purposes it's already serving, and see if there's any way to optimize its performance there rather than trying to "organize" members around some new mission statement. For the latter, creating a new forum with a name/URL, publicity mechanism, logo, etc. suited to the task, then looking for people interested in that task as prospective members, would be a more effective strategy. At most, this forum could provide a recruiting ground for something like that.