Well to be honest andreami I'm inclined to think that some girls just have their own fashion style and girls who like attention will always go after it whether they want to have sex or not.
Most girls wont change their entire style just because they have their period or a yeast infection etc. sorry to go there but those are quite often the reasons why some girls just wont go home with a guy, then again sometimes they do...
I don't want to be one of those guys that says that if girls dress slutty then they definitely want it because there are always exceptions to that rule and as you said some just like the attention, however I would think that there would be a marginal difference in favour of the slutty dressing girls being more slutty... but on the other hand you might be better off going for the non-slutty looking ones just because they are often overlooked by sleazy guys and therefore have less options.
Personally I tend to stay away from the really slutty looking girls because from my experience they tend to have a lot more attitude and bitchiness and when I am out I want to have a good time, I don't want to be babysitting some trashy slut who I don't even like as a person especially when there are total babes there who dress decently and have a personality.
At the end of the day experience has taught me that most girls are open to sex, even if they say they would never do a one night stand, I have gone home with plenty of girls who claimed that and just because they are not looking for a one night stand doesn't mean it wont happen if they meet a guy who excites them enough to make them stray out of their comfort zone.