Perhaps making some % of attacks ethereal would be a nice little nudge for spirit disciple as part of the vampiric buffs.

It always seemed weird to me that reavers, who can wield giant 2-handers and whatnot, can bypass all armor 50% of the time.. whereas a spirit disciple, with faster-and-less-powerful attacks, just has the one punch every minute, and the rest go against armor as normal.. kinda always seemed like the two oughta be swapped if anything!