There might be a trainable skill of noticing high-leverage facts. For example, a friend of mine claims that a modest weekly investment in keeping up with soccer allows him to 'have a good conversation with any man'. In particular example, a basic knowledge of the proceedings of a FIFA World Cup while it is taking place is extremely cheap but might be extremely high leverage depending on where one lives and the demographic distribution of one's interlocutors.

Similarly 'current affairs' (legislation, policy, political manoeuvrings, disasters, humorous stories, etc.)

Also, I encourage this kind of experimentation post.

Since LW is going to get a lot of visitors someone should put an old post that would make an excellent first impression in a prominent position. I nominate How to Be Happy.

Rather, the problem is that at least one celebrated authority in the field hates that, and would prefer much, much more deference to authority.

I don't think this is true at all. His points against replicability are very valid and match my experience as a researcher. In particular:

Because experiments can be undermined by a vast number of practical mistakes, the likeliest explanation for any failed replication will always be that the replicator bungled something along the way.

This is a very real issue and I think that if we want to solve the current issues with science we need to be honest about this, rather than close our eyes and repeat the mantra that replication will solve everything. And it's not like he's arguing against accountability. Even in your quoted passage he says:

The field of social psychology can be improved, but not by the publication of negative findings. Experimenters should be encouraged to restrict their “degrees of freedom,” for example, by specifying designs in advance.

Now, I think he goes too far by saying that no negative findings should be published; but I think they need to be held to a high standard for the very reason he gives. On the other hand, positive findings should also be held to a higher standard.

Note that there are people much wiser than me (such as Andrew Gelman) who disagree with me; Gelman is dissatisfied with the current presumption that published research is correct. I certainly agree with this but for the same reasons that Mitchell gives, I don't think that merely publishing negative results can fix this issue.

Either way, I think you are being quite uncharitable to Mitchell.

When natural scientists attempt to replicate famous experiments where the original result was clearly correct, with what probability do they tend to succeed? Is it closer to 1 than, say, .7?

Ok, here are my reasons:

1) I would like to be able to talk about politics with rational people
2) Understanding more of how the world works could be useful in other areas.
3) I want to be able to make references to things that might be construed as political without having the entire post downvoted to -6 because I'm not allowed to talk about politics.
4) I am increasingly worried about the radicalisation (Assuming it really is increasing) of Less Wrong and I think the problem is that crazy views get too much credence here, due to an unwillingness to criticize by more rational people. (Biggest issue for me)

Edit: I don't get why I receive so many downvotes in a matter of minutes for answering a question as honestly and helpfully as I can manage. I see the same in some of my other posts. I somewhat suspect this is entirely based on party politics, where I am perceived to be criticizing party X in the original post, and so have unrelated posts downvoted by angry people. But maybe I'm missing something.

Ok, here are my reasons:

1) I would like to be able to talk about politics with rational people
2) Understanding more of how the world works could be useful in other areas.
3) I want to be able to make references to things that might be construed as political without having the entire post downvoted to -6 because I'm not allowed to talk about politics.
4) I am increasingly worried about the radicalisation (Assuming it really is increasing) of Less Wrong and I think the problem is that crazy views get too much credence here, due to an unwillingness to criticize by more rational people. (Biggest issue for me)

Edit: I don't get why I receive so many downvotes in a matter of minutes for answering a question as honestly and helpfully as I can manage. I see the same in some of my other posts. I somewhat suspect this is entirely based on party politics, where I am perceived to be criticizing party X in the original post, and so have unrelated posts downvoted by angry people. But maybe I'm missing something.

I think it's a bit silly to call it "courageous" to criticize an online forum. At worst it makes me feel slightly bad when my posts get downvoted as a result. But I appreciate that you are trying to encourage meaningful criticism on Less Wrong, which I feel is badly needed. So thank you for that.

Upvoted for trying to make Less Wrong a better place.

Upvoted because even if the answer is "no," it's still a question worth asking and one that takes courage to ask.

as expensive as raising children in the ordinary way

What about targeted vaccinations and other health interventions for smart kids? I don't think this is a good idea, partly because it's going to be so much less efficient than just helping everyone, but you may. Alternatively tutoring is free and with a similar level of time costs to raising your own children you could tutor a lot of others.

If you think you can produce net-positive children...parents of Isaac Newton, I'm looking at you...

Considered as an altruistic endeavor, you probably do better to find existing kids with the potential to be net-positive and help them reach their potential.