(Though I think the HMC honor code is fantastic, and I’m sure that it is part of the cause of student self-selection: a certain type of person is likely to apply to a school with such a culture.)

Correct, I went to Harvey Mudd.

What you say certainly has some truth to it, and I am skeptical this policy would work for the population at large. However, the other colleges (especially Pomona) are also pretty selective in their admissions, and there is a significant overlap in student life between the various colleges. While Mudd's honor code may not work as well with other student populations, I also think that other regulatory systems would not work as well with that student population. For one thing, it's essentially a college of hackers (in the HN sense), so having a stricter or more explicit set of rules would probably result in "creative" ways of following the letter of the law, with less regards to the spirit.

Can you expand on what you mean? I can't imagine that either test scores or economic status is correlated with jack-assery, although I guess it's possible. If I were forming an experiment, in fact, my hypothesis would be that the latter is positively correlated (but I doubt it would pan out).

Yep. Also I am compelled by ancient tradition to point out that Caltech's style and traditions are going down the tubes due to the shift from administration by faculty to administration by professional administrators. (Note that this has been the received wisdom for long enough that it can't possibly be quite as true as it's made out to be.)