Alright, in all the years I've played CF, I never did go for an antipal, so this view is from the outside of the class, developed over around seven years and spurred by some comments by Sabiene down below.
1st point/question: From what I understand, the AntiPaladin puts a bit of himself/his essence into a weapon when he converts it to an unholy one. Now this would, in my opinion, make it something of an extension of himself/while also tied to him through darker powers(thus the fine penalties when it is destroyed). One thing I have not understood is why the weapons are therefore not made no drop*. This would eliminate many of the, in my opinion, poor strategies developed over the years for destroying one of the weapons and would make them more of an extension of the dark knight himself. Now yes, this makes the weapons harder to destroy of course in some ways, but I have always thought to destroy a weapon you should have to kill the anti-paladin who wields it. Now here consider how painful and difficult it is for an evil to destroy/seperate a paladin from a Defiance even, which is not attuned to him. I guess I see it as he has worked hard to obtain all these charges, everyone should have to work just as hard to take them away, a nice challenge.
*The no drop would be limited to the anti-paladin himself, whereas to all others it would be just as it is now. And this would reflect the AP not willing to part with his weapon short of death, as opposed to these friendly ones handing them out to be Ided and all.
*Perhaps he would need a spell up for this ability, maybe even just the existing spell with those spirits that go into enemies. It could be seen as these spirits not allowing the tainted weapon away from the one it is tied to or somesuch. (Note: If it is a spell it should not be dispellable, as this leads back to cheap tactics and away from the actually killing the AP).

2nd point: A bit different here, but still off of the Dark Powers and Extension of one's self view. Just as the weapon feed's off the soul/mind of the victim, could there be a chance of the weapon feeding off the blood of the opponent during combat? This would be a chance of a minor healing due to the blows similar to a very toned down vampiric touch. A note on this one, I think the dark powers should have to bond with the ap significantly and perhaps it only be available after the ap has learned at least half of the controls for the unholy weapon.

Well, just a couple points off of the Ap's weapon as I've viewed it over the years. I'm sure some people won't like the idea of making it harder to seperate one from his weapon, but I always liked earning your due, not cheap tricking around it. And it would make the weapon more of an extension to the AP.