And maces too. Do they increase your magic power?
Not that I'm aware of. The only think that I know that increases (besides attack power) is evasion. All Maces add +4 to a character's evasion, which is useful in avoiding attacks by an enemy. You can also use a shield with these weapons, which aids in defense (hopefully that's something that you already knew). Any support character that you have that you gear mainly as a magic user would make the most out of this type of weapon.