As I've said time and time again, he's supposed to be a trickster and master manipulator, not a brute force Mage.
I like this definition.
a mage that like his inteligence and his closed library should pay tripple for war and nature!
Or thinking thematically of a "wizard" from pretty much any RPG (pen & paper or video game), why not something that makes him more inclined to wear lighter armour, like:
"Wizard pays triple for non-Arcane Equipment spells."
This way, he's more dependent on Enchantments (and his Voltaric Shield of course) for Armor, and less likely to go with Battle Forge (and if you make him pay triple for War as well, then he'll really think twice about a Forge). This means a big penalty for a Veteran's Belt-based turtle/tank Wizard... which doesn't make sense thematically anyway. He still has some good equipment options in-school - for example, a choice of 3 Rod/Staff weapons + Dispel Wand + Mage Wand, 3 cloaks (Suppression Cloak or Elemental Cloak or the cloak from Academy), Sistarran Robes, 2 mana amulets, several rings including Enchanters, etc. The biggest thing would be that Dragonscale Hauberk and other elemental-based chestpieces would cost 3 sbp, even if he chooses that elemental school (!)... but 3 sbp isn't really a lot to pay (I've always felt they should have cost 2 sbp instead of 1). Oh, and Elemental Wand would cost him triple... which is weird, but probably less weird than a Wizard sporting all the heaviest armours in the game. Besides, he could still exclusively use Mordok's Tome for cheap, which is sort of similar (minus the Spellbind trait). In other words, it really makes him want to focus on Enchantments, Incantations and either hard-casting or Wizard's Tower'ing his attack spells.
That seems a bit over the top. I originally thought that viable alternatives to dispel and teleport for other mages, combined with fixing the tower might be enough. But I'm not so sure now. Maybe should make wizard pay triple for something, but I'm not sure what. He generally doesn't tend to use war spells much, and it wouldn't really make sense for him to pay triple for nature when he understands nature well enough to do experiments on it. Making him pay triple for opposing elemental school doesn't make much sense either. I suppose one could sort of argue that holy and dark are less "rational" and therefore arcane should be opposed to it, except that in the world of etheria the gods actually do exist and this can be demonstrated experimentally. One of them even lives on the moon! So paying triple for holy or dark doesn't work either.
So thematically, what should the wizard's main strengths and weaknesses be?
I'm thinking he shouldn't be super muscular, since he spends so much time researching rather than working out, and he usually wins his battles with his magic, his wits and his strategy rather than his physical strength. He already has only 32 life, the same as a priestess and a force master, which makes sense because the forcemaster uses her mind to fight, and the priestess uses the help of her goddess to fight.
The wizard should not be iron man. He generally doesn't need to wear as much armor as other mages because of voltaric shield. He usually doesn't even use the voltaric shield until nearly the end of the game. So for most of the game one of his main abilities does not see use at all.
The wizard as he is now tends to overpower people through sheer inevitability. He overpowers them by building up a huge mana and action advantage for a relatively low cost compared to other mages. Most effects that raise channeling or mana are in school for him. Most effects that lower opponent channeling or mana are in school for him.
In short, he has a built in mana advantage over other mages. This built in mana advantage should not exist for no reason. I propose that the reason he has a mana advantage is to pay for the voltaric shield, just like the reason the warlock has such a high starting life is to pay for blood reaper. The fact that the wizard can put on so much armor so easily means he rarely has to use voltaric shield, so he has extra mana to spend on other things.
Maybe making him pay triple for out of school equipments is a good idea after all?