I believe CFAR workshops address a lot of these issues, a huge focus of them being the interplay between high-level, logically thought out cognition (system 2) and the lower level, intuitive thinking (system 1). One of the major points was that system 1 is actually very useful at providing information and making decisions, so long as you ask the question right. Smart people I think tend to under-utilise system 1, often ignoring their gut feeling when it is providing useful information.
To use your fashion example, If I consider dressing up nicely, part of me says "This is all pointless, it's just signalling!", and wants me to squash the little voice that is telling me that actually, I value looking nice and should just give in to that desire because there are actual upsides and no downsides!
Again, I found that the CFARian way is to provisionally accept your terminal goals and gut feelings as legitimate, and go about satisfying them rather than criticising them too much (criticising them being a job for epistemic rationality, CFAR being more about instrumental rationality)
I'm hesitant to link you to Julia Galef's "The Straw Vulcan" talk, since everything you're writing seems so in line with it that I suspect you've already seen it! But if you haven't, it's incredibly relevant to this topic.
Another thing I'm reminded of is the post Reason as a Memetic Disorder. Basically, sometimes there are good cultural practises that smart people fail to see the logic behind (because it's subtle, or because it's inconsistent with some false belief they have), and so they drop the practise, to their detriment. Less smart people keep doing it, since they're happy to simply conform without having reasons for everything.
While LessWrong contains a large amount of high-quality material, most of the rationality advice isn't actually targeted at our core audience. The focus seems to be more on irrational things that people do, rather than irrational things that smart people do. (Sidenote: If we wanted to create a site focused on spreading general rationality, then we'd need to simplify the discussion, remove a lot of the maths/controversial ideas and add in some friendly images. Does such a site exist?).
This has led to a number of comments questioning the real world value of having read the sequences. If your average person had the patience to read through the core sequences and understand them, they'd find them extremely valuable. It'd provide them with a glimpse into a new way of thinking and even though they would likely hardly appear to be very logical to most Less Wrongers, they'd be much better than they were at the start.
On the other hand, most Less Wrongers already know the basics of logic. That's not to say that we don't act extremely irrational much of the time, but just that going over the basics of logic again probably provides minimal benefit. What is needed is something specifically targeted at the kind of irrational mistakes and beliefs that intelligent people make. I would argue that if this were a sequence, it would be the most important sequence in the entire site. But, since I lack that level of writing ability, I'm not even going to attempt such a project. So I just created a post where we can list articles or ideas that should be part of such a sequence in the hope that someone else might pick it up
Here are some examples of mistakes that intelligent people make:
Taking a fixed instead of a growth mindset - shying away from challenges, convincing oneself that we are just naturally bad at non-intellectual things and that we shouldn't focus on them
Directly pointing out people's flaws
Overthinking issues that are really very simple
Counter-signalling by ignoring the value of fashion, money, being liked
Valuing intelligence above all other qualities
Rigidly adhering to rules
Expecting other people to always be rational
Not considering popularity as a signal that is worthwhile understanding
Overvaluing being right
I'm sure there are plenty more. Any other suggestions or relevant articles?