I've been toying around this idea about weapon damage type and armor as AC or DR.
Under 3/3.5 rule;
When you roll higher than AC, you deal full damage. Armor doesn't reduce damage at all.
When you roll less than touch AC, you miss, so you deal no damage. Armor doesn't matter.
When you roll higher than touch AC but lower than AC, you deal no damage. You touch your target, but his/her armor reduce damage completely.
Then, how about "you deal partial damage when you roll higher than touch AC but lower than AC"?
You graze your enemy, his armor soaks some force , but you somewhat hurt the enemy.
"Partial damage" can be simply "half damage." Just halving numbers isn't that hard, I guess.
Or each weapon could have both "full damage(when hit)" and "partial damage (when touch)" to represent damge type.
Like, a sharp blade has higher full damage but much lower partial damage, and a mace has decent full damage and not-so-lower partial damage.
Adding "critical damage" for each weapon is also possible.
With this rule, armors should have higher AC bonus (and small "touch AC" bounus), for damage will be dealt more frequently.
Also, you can't roll damge and atack roll at the same time. This can be small drawback.