X-Rationality can help you succeed. But so can excellent fashion sense. It's not clear in real-world terms that x-rationality has more of an effect than fashion. And don't dismiss that with "A good x-rationalist will know if fashion is important, and study fashion." A good normal rationalist could do that too; it's not a specific advantage of x-rationalism, just of having a general rational outlook.

Yet many highly intelligent people with normal rationality have terrible fashion sense, particularly males, at least in my anecdotal experience. Ditto for social skills, dating skills, etc... (fashion is really a subset of social skills, combined with aesthetics). (a) Are these people not really rationalists, because they haven't figured out how to improve themselves in those areas, or (b) do ordinary rationalists have trouble figuring out that they would benefit from improvement in those areas, and how to do it? Or perhaps (c), they recognize the benefits of greater social abilities, but they do not believe that the effort is worth it?

In principle, normal intelligent rationalists could figure out how to improve their fashion skills and social skills deliberately and systematically. But if indeed so few people in that category do so, I would take it as evidence that a systematic approach to developing interpersonal skills and style actually requires a higher level of rationality that what normal rationalists possess (perhaps x-rationality, depending on what we mean by that).