I would give the opposite advice. The easiest thing you can do to make people like you more, trust you more and respect your opinion more is to dress well and appropriately.
Job's outfit and Zuckerberg's hoodies work the same way (whether that was the intention or not, I think not). The same part of human brains that stupidly subconsciously judges people by the way they are dressed is doing the same thing with them. They show status by being able to openly reject the standard social expectations around clothes.
So call it a psychology hack or a life hack or whatever but if you are a founder of a startup then you are meeting and needing to impress a fair number of people. You can handicap yourself because you are convinced that it "shouldn't matter" or "this is the startup uniform" or you can be pragmatic about it and gain an edge for relatively minor effort.