This has never been true and will never be true for one very important reason: limited attention span. No one has an infinite attention span, and there are many stimuli competing for our attention. Thus, when someone shows up looking like a hobo claiming to have discovered the secrets of the universe, or someone decked out like a bimbo wants to talk about their latest art project, people rightly tune out. That doesn't make them bad people, but it does mark the person trying to get their attention as being painfully unaware that having knowledge of rhetoric is not optional if you want to succeed.

What you wear when you're not trying to convince anyone of anything is your own business, but when you're actually trying to reach someone, maybe it's not asking too much to demonstrate some basic self awareness? If you're not willing to go that far then why should anyone listen to you?