I think that BOTH men and women have to be physically attractive to a potential mate or their partner. Quite often physical attraction has to be mutual in order for anything to flourish. I realize that women tend to do a lot more to prepare for a night out or date, but that doesn't mean the man is without some responsibility as well. I think it's safe to say that hygiene is a mutual requirement.
Generally, women do have to do more shaving, such as legs, armpits. A lot of them wear make-up, but it doesn't necessarily mean it's a necessity for him as it my be for her. Perhaps she wears make-up to make her feel better and more confident about herself. In that aspect, just because it's seemingly a requirement for her doesn't mean that it's a requirement for him. He may admire her for her natural look.
Hairstyles differ between genders. Some guys wear their hair short, and the fact that they're guys, pretty much limits the various hairstyles a guy can explore. For the guys who do wear their hair long, it's just a matter of keeping it neatly groomed and presentable. Women's hairstyles on the other hand are generally more expressive. They have so many different variations in order to achieve the desired look. The time spent on their hair is often determined by what style they wish to wear their hair in.
Clothing for guys is a lot simpler. Guys basically need to make sure that their outfits are presentable and don't clash between styles and colors. We don't need to make sure the earrings match the color of the outfit. Women often do this as well as other accessories, like bracelets, bangles, shoes, purse, earrings, necklaces, rings all have to blend in somewhat to the outfit they're wearing.
Then depending on the theme of the date, the outfit, will determine the shoes. Color and heal length. If they want to showcase their legs, then they may opt for higher heels. If they're dressing for comfort then it's flats or a lower size heel. Guys generally just need shoes to match the outfits and high tops just don't really change the physical image of the guy as much as heels do for women.
Then there's the decision of what to wear. Guys tend to have a general idea of what they're going to wear because our wardrobe options aren't as vast. Women tend to always be second guessing their select outfit because they want to set a certain image and look the best they can.
I don't know of any psychological or scientific reasons why we all do what we do for the perspective mate. I do know that while guys are concerned about their image, it's more of a self pride and a certain look or style he likes to project or feel comfortable in and his concern is only for himself and his date. Women seem to be more concerned with how they see themselves, how their family and friends, other women, almost society as a whole see them. They want to be unique and stand out. Rarely will you see guys get upset because another guy is wearing a similar shirt