You'd still roll a chance to parry with the shield, though right? You'd just always get 'hit' on the melee defense roll, then have your chance to parry. Not that I'd run with that, (esp for a pvp temp, since that is what the thread is about) but like you said yourself Lord GOD it is a standalone skill. Mystic mage is cool, very viable in pvp as I understand, but don't tell me you aren't using a mage wep!
And in answer to Synbad's question a few posts back, you can definitely wrestle with a shield. The game only checks for any weapons equipped before applying your wrestle to melee defense.
Another interesting thing to note--that only slightly deviates from the subject, lol--if you are using a shield as a 'stat stick' without any parry skill, the durability will last a long, looong time.