You could also just put a normal +1 enhancement bonus on the weapon. That bonus helps with disarm attacks and every other attack -- and it increases damage, too. All in all, it's probably better to have a +2 weapon than a +1 weapon with the Disarm ability.
The Greater Magic Weapon changes this calculation. With a high level caster, you're better off with that +1 weapon with the Disarm ability -- and buffing up with GMW to increase the enhancement bonus above +1.