I don't think it will matter either way. If you dress "to the nines" you might get a guy who is more confident in himself or you might get one that's a player and thinks he's all that and can get anything he wants. On the other hand, dressing "casual" you might get guys who think your easy or lack self-confidence because they don't see you as someone out of their league. You could also find a guy who is more genuine and down to earth.
I feel if you dress to with the level of style you would wear everyday as well as be a reflection of the type of person your looking for, you may have better luck. Many have heard the advice, "be yourself" in this case I would say, "dress yourself." Of course I usually wear a T-Shirt and sweat pants around the house so what do I know about style lol.