Since you helped answer my question about the 3 cases, I'll return the favor.
My short answer is YES, I do care how the girl dress like.
Things like clothing, hairstyle, make up, body language, and tone of voice all give hints to what the girl is like inside. Or at least they tell me how this girl see her self in society and how she presents herself.
So in the case of dressing up and looking all "nice" as you put it, some guys, I am one of them, might draw good/bad conclusions about the girl based on this and of course a few other things listed above about self-presentation. But generally, girls who dress up like that are either the high maintenance type or has high expectations of who gets to date her. Dressing up may make look good/better, but the messages you are sending out may work against you.
Dressing down, the casual stuff, has its pros and cons too. If you dress down a lot, then people might think you are a down-to-earth type of person, which of course is good. They might think you are secure and low maintenance. But at the same time, they might think you are the type who doesn't take care of herself, who might have no sex drive.
So what's best? I recommend doing both. Yep! Go random... You can try dressing casually with jeans and tanks for maybe 3-4 days in a week, then suddenly out of nowhere, appear in those sexy shirts/dresses one day. If anyone, especially the guys ask you why you dress like that, simply answer because you feel like it that day. You are now unpredictable, spontaneous, and perhaps modest in terms of how you flaunt your wardrobe. =)