Layering should give you a bonus as it increases every criteria anyone has mentioned here, weight, resticts movement, and certainly has historical precedence and factual measurables that clearly show that leather over padded, leather over chain, chain over padded, or even leather over weaved bamboo are much more effective. I was watching the history channel just this weekend and they had a weaved bamboo shield covered in a thin hardened leather that was about 4.5 feet tall and about 3.25 feet wide at it's widest and was tapered in the center(weapon weilding). It actualy did a better job of stopping arrows and piercing weapons than a steel shield of normal thickness for that size. Why? because of a little thing called surface tension. It takes alot more energy to break through the outside of something than to continue to move through it. Every layer increases the # of times that the object must puncture the outermost molecules. It works the same for bashing weapons, it would take more and more energy to bend the layers, hence the can't fold a normal sheet of paper more than 8 times thing.
Why wouldn't leather over leather or chain over chain give a bonus too? It also fufills every one of the criteria that have been mentioned in this thread as to what makes a difference in armor categories.
Coolness factor bonuses are a little too subjective IMO, that can come down to preference in style. The 1 exception I could see to that would be wearing a full suit of plate, which I could see giving a person 1 bonus armor pt. I don't think having props should give you a bonus, it could get really ridiculous and that would be purely subjective as to what quanity and quality gives you a bonus.
For chain leave it as is both medium and heavy. The type that only goes to the waist, has no sleeves or the sleevelets is med no matter what it's made of. The kind that covers the crotch and has long sleeves or the kind that has 3 layers of rings is heavy. If you make some 1 inch diameter rings with no backing at all and then try and rules lawyer your way into med you are breaking the "no cheese" rule and should get slapped for stupidity.
If the GM looks at your armor and has any question about it they can call over 2 other GM's and make a final ruling or give you a field ruling and tell you that you need to get an official ruling when 3 GMs are together.
We already have the systems in place to cover all those scenarios and concerns about getting hosed or whatever so use them. If the person cotinues to whine about their armor and such after 3 GM's rule on it then would anyone really care if they continued to complain about it?
Edit: The phys rep bonus thing made me think of the scene in Office Space where the manager and whatsherface are having the minimum flair conversation.