If I may offer up a suggestion to the % chance of spell failure.
I can see how the main point here is to allow necromancers to be less severely impacted by use of this particular armor. What I'd suggest is that the lesser % chance of failure only apply on spells cast from the Necromancy school. Spells from all other schools would still suffer the full chance of failure. I think this balances a bit better, particularly if you'd allow any of these armors to become magically enchanted.
In part, this stems from what you define as a "necromancer", too. Is this a variant class, a specialist wizard, any of a number of prestige classes, or something else? Just curious.
Overall, though, I like the concept. I could see players getting all creeped out when coming across a chap wearing clothing and armor made from the flesh and bones of their fellow missing villagers. *shudder*