A few observations on this subject:
1. When striking any other kind of held, worn, or carried object, you must beat an AC of 15 + the bearer's Dex modifier + its size bonus + the bearer's magic deflection bonuses (15 being 10 plus the +5 bonus you get for being able to move a held, worn, or carried object "quickly out of harm's way").
When striking a weapon or shield, you must beat an AC of a d20 + the bearer's Str modifier (Dex modifier if they have Weapon Finesse and want to employ its bonus instead) + the bearer's base attack bonus + the bearer's size bonus.
Does anyone think it is unusual how different the two checks are though a weapon or shield is much like a held, carried, or worn object?
2. When calculating damage against a weapon or shield, don't forget to factor the following:
* immune to critical hits and sneak damage
* take half damage from acid, fire, and lightning
* take quarter damage from cold
* adjust damage according to how effective a weapon should be when striking another weapon or shield (e.g., cut a net with a club? I don't think so)
3. There seem to be no spells other than mending to fix broken weapons and shields. The description for mending gives no details on how much damage it mends. You can't cure or heal them, because they aren't living creatures.
4. Re: Greater Magic Weapon, it's possible to enchant a weapon so it can sunder your opponent's weapon. Your opponent, however, can do the same thing. You're worried about losing your favorite magic weapon and not having a backup weapon. How about using another weapon enchanted with Greater Magic Weapon as a backup weapon?
5. How easy might it be to destroy weapons and shields with spells? A high-level maximized fireball can do enough damage to destroy anything, especially flammable items. There seem to be no guidelines on whether spell damage works against magic weapons or not.