Maybe the effect only goes off if like the little message comes up saying, "Chizzle blocked the Mob with his shield." and ice spikes will go off. So probably high AGI will see to more ice spikes going off.
I would have to agree with Samanosuke, that the effects probably have a chance to go off when you block with the shield. But, it probably only has a chance of going off at that point, and I no longer get the shield messege, it might be my filters but I doubt it. I think they took that out when the shields stopped blocking all the DMG when they trigger.
umm i think he isnt. this is after all a +1 item that requires a very high alchemy lvl. it is made from an item which on my server is 600k and lastly it is a +1 it might even be more than 1 mil gil look at hawkers +1