Wearing something glamorous makes you feel glamorous. Wearing something current and trendy makes you feel like you're a member of a secret club.
This article identifies some of these things, which I have felt too. It labels the psychology of fashion so explicitly, and even brings in the gender gap into it. Why are men so into sports? I have no idea. Why are women so into fashion and looking good? That I can understand, but a lot of men cannot. That's so interesting!
In the end, it's all about how expressing yourself makes you feel. You can wear whatever, it's how it makes you feel. If you can rock a potato sack like Lucy Ricardo, you wear it proudly. ...That brings up another interesting thing - the tv show mocked Lucy for that, for her expressing herself. The tv show and media at that time (and still today, just less) were run by men. Sports were never ridiculed like Lucy's fashion was. ...Interesting. Again, proof of the gender gap between women's and men's interests.