Fashion isn't prioritized in many hyper-analytical circles. Many in these communities write it off as frill and unnecessary. They say they "just dress comfortably" and leave it at that.
To me, that seems like a huge blind spot. It misses a fundamental point -
A piece of clothing is fundamentally a tool.
Definitions are important so everyone is on the same page. I feel like Wikipedia's first sentence on "tool" accurately describes it -
A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process.
Clothing clearly fits that definition of a tool.
Appropriately chosen clothing can keep you from freezing in the winter, from getting sunburnt in the summer, and can keep you dry in a rainstorm.
It can also help you achieve things involving other people. I think it's fair to draw a distinction between "clothing" and "fashion" based on whether your objectives involve interpersonal skills. If you're wearing clothing in relation to the environment and without other people, that's using clothing as a tool.
But clothing clearly can affect other people's opinions of you, willingness to accept your arguments, willing to hire or contract you, even their desire to associate with you. All of that is changed by clothing - or more specifically, your "fashion."
While most rationalists would happily and quickly plan out the best hiking boots to wear to not get blisters on a hike, or research the best shoes for bicycling or swimsuit for swimming, anecdotally many seem hesitant or even hostile to the idea of using fashion as a tool to achieve their objectives.
That's possibly a mistake.
The thing fashion can do best and most fundamentally is affect a person's initial first impression of you. Fashion is less important if you're in a context where you're guaranteed to get to know someone over a longer period of time, and is more important if you're going to get filtered quickly.
I propose that the most rational usage of fashion is this -
1. Ask yourself what your goals are in the situation you're about to go into.
2. Ask yourself what first impression would help you reach your goals.
3. Pick out and wear clothing that helps communicate that first impression.
The process is important. In isolation, there's no "good fashion" - it depends on your objectives.
In some circles, people more or less won't care how you're dressed. But even then, there's likely some clothing that will perform better than others. If you can afford the time or money to find clothing to fit your objectives, then there's no reason not to utilize this advantage.
I say "time or money" because you can deploy either - if money isn't an issue, there's stores where the majority of things look good, and the people there are professionals who will spend time giving you good feedback. Any high end department store like Saks Fifth Avenue, Bloomingdales, or a high end tailor fits this category.
Alternatively, you can deploy time. To do that, survey the people that most effectively communicate the first impression you want to convey. Take actual notes and look for common trends. Then, go find pieces that look similar. You won't be perfect right away, but like any other skill, with practice you'll rapidly improve. Incidentally, the marginal cost to produce clothing is incredibly cheap, so most fashion lines over-produce clothing and have to liquidate it at super-discount sale prices periodically. There tends to be a major "Summer Sale" and "Winter Sale" once per year that have high end clothing that 70% to 90% off, making the cost comprable to the mid-tier.
There's also "Sample Sales" where over-produced items are liquidated or when a designer wants to see the buying public's reaction to their new pieces. Again, ultra-high-end clothing can be purchased at discount rates at these environments. You can get basically any semi-standard piece of high end clothing for not very much money if you put in the time. My strategy in the past has been to wait until finding a great opportunity like that, and then buying 1-2 years worth of clothing in one swoop. It doesn't take much supplementing after that.
It takes very little cognitive energy to begin this process. Next time you see someone who strikes a very good impression, stop and analyze a little bit. Note what they're wearing. If you want to strike that same first impression, go get something comprable. Your fashion will be working for you at that point, and your interpersonal dealings will become easier.