"Dressing down" to impress in academic settings

If an academic is dressed in an unusually casual manner, I generally ignore it.

If an academic is dressed in an unusually formal manner, I assume one of these:

• They are an administrator, or manager, rather than an academic
• They are here for a job interview and they don't know it is not necessary to dress formally
• They are going to an event outside academia, like a funeral

I do not think anyone is impressed by either dressing up or down, but it can send a signal.

This is just a complicated race of mind games.

There are many fields where 'dressing up' is the norm, as it gives a first impression of respectability and competence. This is also because in many fields 'dealing with people', being sociable and looking professional and respectable is an integral part of the job.

In the hard sciences, on the other hand, your results speak for you, there is limited interaction with people necessary, and it is widely recognized that "dressing up = being good" is a false association; no amount of tailored suits will hide the fact that you don't know your stuff. The two things are completely orthogonal. Also, many scientists are not 'people persons', to put it mildly.

So when you overdress, this raises a warning in the mind of many scientists: 'Is this guy one of the many people in the world and in other fields who dress up as an attempt of hiding their incompetence? I should be careful in judging him'. But there is nothing inherently bad about it if you really are competent at your job, and you can let your work speak for you. Some scientists routinely suit up for conferences.

Similarly, dressing down is not seen a problem, as long as basic hygiene norms are respected; at most it can raise an eyebrow.

Let me add a German perspective, biased by an interdisciplinary field of computer science where "the other discipline" is more formal than CS.

• In day-to-day life, students, doctorate students and post-docs are dressed as they would do in other aspects of life. Some are more dressed up, others dressed down, nothing special. But no one would appear in a suit or nice dress (like e.g. in economics / law where it is quite common in Germany)
• Professors are usually dressed a bit more formal, also depending on the field. In general, the closer they are to economics / business studies, the more formal the dress. I usually attend in a jeans / shirt combination as long as we don't have guests or formal ceremonies.
• In formal settings (guests from industry, formal speeches, interviews, ...) a suit / business dress is common, for most a tie as well.
• In conferences, it's about the same, but the range is broader. Some dress up a bit more then usual (e.g. most presenters wear a suit / business dress). I personally would recommend this (and recommend it to my PhD students), because it shows some kind of respect to the audience. But maybe this is because I have a background in performing arts as well and stage presence is a must there ;-). If someone is dressed informally, I personally don't care.
• In contrast to some answers, in Germany I would highly recommend to wear a formal dress in job interviews at least for faculty positions. For PhD candidates / postdocs it is not necessary.

I never heard of someone dressing down intentionally.