Recently I've been musing about the fact that armor and weapons are boring stacks of numbers in D&D. Actually, most games that don't use rules-light weapons are kinda boring, and there's the fact that there will always be weapons and armor that are just plain better than the other choices, from a plain numerical standpoint.
So what if weapons and armor didn't give a bonus or penalty in and of themselves? In this happentrack, you'd have, for example, an Armed and Armored set of conditions.
So, I dunno, normally you can only deal 1d3 Nonlethal damage with melee attacks, which provokes an attack of opportunity. If you are Armed, you instead deal 1d8 lethal damage, and your attacks don't provoke AoOs. Similarly, let's say the Armored condition forces the person attacking you to roll twice on their attack rolls, taking the worse result.
However, weapons and armor have tags. Tags don't do anything by themselves - they are just places to hang mechanics off of. To an untrained person, wielding a dagger and wielding a greatsword are identical.
To an untrained person - if you're Proficient in weapons with the [Sword] tag, you might ignore the Armored condition of someone wearing [Leather] armor while wielding a [Sword]. If you have Power Attack, you deal 2d6 damage when Armed with a [Two-Handed] weapon. If you have Weapon Focus in weapons with the [Axe] tag, you can do a badass cleaving attack. Stuff like that.
Clever modifications of your weapon (shove your sword in burning pitch to fight ice monsters!) might add tags temporarily, allowing you to bypass the ice monsters' resistance to non-[Fire] weapons.
In other words, it doesn't matter what hunk of steel or wood you picked up - we're fighting a dragon here. What matters is what you can do with it.
I'm also musing that the bonuses would have to either be active stuff or situational bonuses, just for the purposes of adding some variation in combat. Add in a system for expanding your training in weapons horizontally (think Weapon Aptitude), and I think it could work out well.
One last note: being magical would be a binary condition under this system. That way, your magical sword that you found at 4th level will still be relevant when you're 12th level.