The fact that it only gives half your crit chance to spells seems ludicrous, especially since unlike regular attacks, spells actually have cooldowns. The only way I've seen a reliable way to make this work it to pair it up with enrage, a Warfare ability which works against Elemental Affinity and only lasts 1 turn.
It doesn't even work, I tried it but I never crit out of 10 or 20 attempts so I don't think this is even an option.
The problem with spell that crit is that source spell are already very strong, if they reliably crit, you use one spell and that's it.
I have just finished the Alpha build again with 1 2Hander crit build Warfare, 1 Rogue, 1 Aero/Hydro mage, 1 Necro/Geo mage.
On the Alexander fight I just teleport every enemy in the same location more or less, (the Necro has the teleport gloves), used chain lightning from an elevated spot and everyone died except for the bishop and the caster (which were badly hurt. The worm had not appear yet.)
So add a crit to that and even the boss would have been done which might be too strong if you do it reliably.
On the other end, my Melee guy had 34% crit chance. So if you build a Crit caster you would still have 17%. which is decent but you don't really count on that.
