The vast vast majority of harmful paladin spells are instant cast and so won't benefit from the proc. If you want it for the spell damage then there are much better ones.
It doesn't proc on healing spells, and it's 1H so if it'll gimp your melee DPS if you try it, so the only way I can possibly imagine this would be useful for a paladin is for a hybrid tank/healer that casts healing spells when it procs, which is a ridiculous corner case.

I think it's safe to say if you're a paladin and think you have equal precedence to a primary spellcaster on this then you're either a ninja or deluded.

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Youre right, Pala's need +dps. But the Blade of Wizardry is definatly not AMong Tankadin, or DPS-adin weapons. A Tankadin would need a much heavier sword with way more Stamina, more damage, and either agility or defence rating, this sword is made for one thing and one thing a lone.

"Casting Ranged spells"

And even so, not a good sword at that, better to farm a Gladiator war staff