The word dresses has two meanings.  One meaning of dresses is a verb signifying the act of putting on clothing.  Another meaning of dresses is a description of the results of dressing.  Specifically, dresses implies an average or long term judgement about a persons sucess in putting on clothes that look attractive.  The word dressy discribes clothing that is attractive and that in the language of clothing expresses the idea that the person wearing the clothes is wealthy.  Dressy clothing typically has a higher cost.