A weapon that does extra damage to living creatures would be "almost" as good as a weapon that does it to all creatures. I think it might border on the Unholy ability, that does increased damage to good creatures (which seldomly include undead), though im not sure.
The ability to hurt incorperal undead is called "Ghost Touch" in the Dungeon Masters Guide If im not wrong
I like the concept of animating the slain enemies. I had already been pondering about it, a weapon that animated a slain enemy as a zombie 1d6 rounds after he had been slain. The Ghoul version of the weapon would be more expensive off course. I was thinking the Zombie version should be +2, the Ghoul version +3. You could then turn the Ghoul Toxin into a separate ability, for a +1 cost perhaps, since its not overly powerful. I prefer to break abilities down, as it allows for greater variation.
How about this, something I dont think people have thought about before....
Life-Slaying: An ability that reduces the weapon market price by -1. Thus, you could make a +2 Longsword with Life-Slaying and it would only cost as if though it was a +1 weapon. It should though be impossible to make a weapon cost less than the price of a +1 weapon. Life-Slaying alters the magical abilities of the weapon so that they only affect living creatures. Thus, you could make a +1 Keen Longsword Lifeslaying. Thus, it would cost as a +1 weapon only, but would be equal to a +1 Keen weapon against living opponents, but only a normal Longsword against undeads and constructs.