Yaakov Doe:- Correction:- One should dress as if it were Shabbos, but on Yom Tov wear even finer clothing than on Shabbos or Chol haMoed.
In practice, one basically wears Shabbos clothing, but with some weekday clothe, in view of differing opinions, although for sure, in much better attire than on an ordinary weekday.
In practice, I wear Shabbos suit & ties, but weekday shirts, as don’t have enough Shabbos shirts, considering for sure, no laundering on Chol haMoed.