No, not at all. My girlfriend will dress up sometimes and she looks smoking hot, and I will tell her so. We have gone dancing and she's worn cocktail dresses and stuff like that.
We have also just gone to the movies, hung out at home, or went to play poker with friends, and she wore soccer shorts and a tshirt, short shorts and the girly tank-top thing, still looking absolutely amazing and I tell her so then too.
Personally I prefer girls who are casual about that. I'm not someone who will notice necessarily (I know shame on me), and a girl who stresses about dressing up and worries about make up every time she leaves the house will get annoying. Someone who dresses up for every occasion down to going to a grocery store will give me the impression of high maintenance. I'm not saying that you shouldn't take pride in how you look, but you don't have to be vain about it.