Either one of us is wrong about their client base, or else "wealth" is not an indicia of what someone expects or wants to see in their service providers. I suspect it is the latter. Therefore it is not that when selling services to rich people one should dress expensively or modestly, but that in different lines of work there are different standards and expectations. I'm sure your style works well in your field just as I'm sure mine works well in mine, even though we could have some overlap in clients.
That is my attempt to reconcile what you see on a daily basis with the reaction you are perceiving here.