I think you have too limited a picture of what searching for truth entails, and that we don't have as great a difference between our views as you think.
Newton and Einstein used rationality to seek truth and bring unity to experience, not for practical results. But they were both smart enough to know they'd better check their results against experience, or they'd get the wrong answer and never be able to move further. If we're smart, we'll do the same, whether we're after truth or whatever.
Someone once said there were two kinds of rich people - those who really like having luxury goods, and those for whom money is just a way to keep score. The same could apply to rationalists; there are those who want some specific practical goal or predictive ability, and there are others for whom the ability to achieve practical goals or make predictions is a way to keep score. Einstein was happy to hear his theory successfully predicted the path of light during an eclipse, I'm sure, but not because he was in it for the eclipse-light-predicting.
Newton and Einstein used rationality to seek truth and bring unity to experience, not for practical results. But they were both smart enough to know they'd better check their results against experience, or they'd get the wrong answer and never be able to move further.
...In 1919, Sir Arthur Eddington led expeditions to Brazil and to the island of Principe, aiming to observe solar eclipses and thereby test an experimental prediction of Einstein's novel theory of General Relativity. A journalist asked Einstein what he would do if Eddington'
Robin wrote how being rational can harm you. Let's look at the other side: what significant benefits does rationality give?
The community here seems to agree that rationality is beneficial. Well, obviously people need common sense to survive, but does an additional dose of LessWrong-style rationality help us appreciably in our personal and communal endeavors?
Does LessWrong make us WIN?
(If we don't WIN, our evangelism rings a little hollow. Science didn't spread due to evangelism, science spread because it works. Art spreads because people love it. I want to hold my Art to this standard. Push-selling a solution while it's still inferior might be the locally optimal decision but it corrupts long-term, as many of us have seen in the IT industry. That's if the example of all religions and political movements isn't enough for you. Beware the Evangelism Death Spiral!)
We may claim internal benefits such as improved clarity of thought from each new blog insight. But religious people claim similar internal benefits that actually spill out into the measurable world, such as happiness and charitability. This fact gives us envy and we attempt to use our internal changes to group together for world-benefitting tasks. To my mind this looks like putting the cart before the horse: why compete with religion on its terms, don't we have utility functions of our own to satisfy?
No, feelings won't do. If feelings turn you on, do drugs or get religious. Rationalism needs to verifiably bring external benefit. Don't help me become pure from racism or somesuch. Help me WIN, and the world will beat a path to our door.
Okay, interpersonal relationships are out. Then the most obvious area where rationalism could help is business. And the most obvious community-beneficial application (riffing on some recent posts here) would be scientists banding together and making a profitable part-time business to fund their own research. I can see how many techniques taught here could help, e.g. PD cooperation techniques. If a "rationalism case study" of this sort ever gets launched, I for one will gladly offer my effort. Of course this is just one suggestion; everything's possible.
One thing's definite for me: rationalism needs to be grounded in real-world victories for each one of us. Otherwise what's the point?