Improved sunder is kick ass when you face foes who do not use uber magical weapons. Say sticks, wooden shafted weapons etc. Also somecases you cannot sell the loot (also; would a blackguard sell holy avenger which could serve cause of good another day and face another hero wanna be with it? Better destroy or corrupt said artifact).
So sell it to an evil temple (for half its market value) that will use it in a corrupting ritual...I didn't say sell it at the Magic Mart.
If your enemies have non-magical weapons and you do, you outclass them to where letting them keep their stuff while you kill them won't hurt. A feat that's only good for 2 levels...isn't a good feat.
Also improved sunder can work other cases like severing head of a hydra, or sever tentacles, sever armor belt straps (and note; easy to repair and does not damage a weapon) to make it fall apart (and get nude view of female paladin without breastplate). Improve sunder vs mage's wand (wand is useful someone else in your party but what blackguard cares for another party members? LE one would prefer destroy mage's wand and strip it's only offensive spell spam method).
-I'll give you the hydra, but that's the only situation where you would want to sunder.
-Cutting people's clothing off is a nice idea in Japanese manga/anime sex comedies, but if you're actually fighting for your life against a dangerous enemy, you should have bigger priorities than clothing damage (ignoring the fact that said paladin would probably have a shirt on underneath). While this is going to be an erotic/extreme game, I do not get the feeling at all that it's meant to be a humorous one...and I don't want it to be, that would spoil the mood.
-A blackguard who doesn't care about his party members' needs is a very short-lived blackguard, because there are more of them than him and he can't keep his back to a wall 24/7. Evil doesn't have to mean 'ignore everyone but yourself', it means 'You are Number One' - Evil people can have allies and even friends. And what better way to piss off the party wizard, who has 9001 ways to make a melee-warrior like you suffer horribly, than breaking his loot?
-If a wizard is spamming spells from a wand...he's a bad wizard and should die (or he's out of prepared spells, either case means he is no longer a threat). For that matter, any defenses a wizard puts up versus melee attacks will affect his gear, so if you can even try to sunder his stuff in the first place, sunder him instead, and by sunder I mean chop in half.
Improved sunder can be applied other situations than just 'sunder held weapon'. Of course it's situational but these pop up regularly often enough that able break things without AoO is nice.
You don't need Improved Sunder to use the Sunder action, it just removes the AoO. And sundering an enemy's non-weapon gear is an even worse idea than sundering their weapons, because it also reduces your loot while not affecting their ability to kill you as much.
Or my group house ruling; you can try sunder foe's arms (or legs) instead weapon if you want to with improved sunder but it's harder than try breaking a weapon because HP needed to breach through to mutilate a foe.
Eewww, called shots.