No idea, since attack doesn't work with spells, but you mean some sort of potency bonus or a "blue magic physical attack+" thing right? I don't know the numbers needed to calculate the damage. But my thinking is, if it affects physical spells, it could be a way for BLU/NIN or anything not /THF to damage high defense or higher level mobs without SA, particularly with multihit spells.
But it could be lame (relatively) and just be some sort of attack boost like the monk JA. Still would be nice though for a WS.
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