First some fictional evidence.
For one it is really hard to create a homogeneous community. The libertarians try for a while, and maybe you can by a seastead some day. But you would still give up a lot. Then there is no real need to have a society consisting only of rationalists. There are many jobs that do not need a full blown rational person, so you always have some other people doing stuff. Probably a majority. You need some great minds in the right places, that is all.
Then there is the tendency that great minds often have trouble getting things done and this. Very bright people I met often achieve things because of their respective support network that takes care of more mundane things.
I experienced the occasional talk out while putting some project together, when action was required.
From the other angle I wonder how much reason can actually be implemented on a wider scale. I get the impression a lot of advancement was achieved by pumping the right cached ideas into the population. And then you meat decent programmers who are creationists, or into homeopathy.
Lets collect some ideas on how to achieve it.
I think that the greatest barriers to creating an above-average IQ, above average rationality society are realpolitik-based, rather than some theoretical failing about how smart people can't do practical stuff.
Think about it on the margin. Garret Jones has basically porved from existing data that +1 IQ point = +15% GDP per capita (or something of that form).
I'd expect that an average score increase of +0.1 on the cognitive reflection test would have a similarly large effect on getting rid of creationism, bad economic policies like protectionism, etc.
Last Wednesday (2010 Dec 01), BBC Radio 4 broadcast a studio discussion on the question: "should we actively try to extend life itself?" The programme can be listened to from the BBC here for one week from broadcast, and is also being repeated tomorrow (Saturday Dec 04) at 22:15 BST. (ETA: not BST, GMT.)
All of the dreadful arguments for why death is good came out. For uninteresting reasons I missed a few minutes here and there, but in what I heard, not one of the speakers on any side of the question said anything like, "This is a no-brainer! Death is evil. Disease is evil. The less of both we have, the better. There is nothing good about death, at all, and all the arguments to the contrary are moral imbecility."
Instead, I heard people saying that work on life extension is disrespectful to the old, that to prolong life would be like prolonging an opera, which has a certain natural size and shape, that the old are wise, so if we make them physically young then old people won't be old, so they won't be wise. Whatever cockeyed argument you can construct by scattering into a Deeply Wise template the words "old", "young", "wise", "decrepit", "healthy", "natural", "unnatural", "boredom", "inevitable", "denial", I heard worse.
If I can bear to listen again to the whole thing just to check I didn't miss anything important, I may write something on their discussion board.