Oh, and another thing to consider with schools for high level PCs - Simulacrums. What schools make the best simulacrums? When your simulacrum runs out of spells and is down to cantrips and at will abilities, which ones are the most useful as a simulacrum? Not all wizards will make simulacra, nor will they always make them of themselves, but many do. The simulacra of wizards can cast rituals, use cantrips, use school based abilities, etc...
THat's an interesting thought experiment. I am currently playing a 12th level illusionist. On his fingers he has illusionary rings, each created with a major image spell using a 6th level slot (permanent until dispelled). He can use Malleable illusions to change those rings into the illusion of his choice by using an action, then turn it back into an illusionary ring afterwards.
I'm thinking a Simulacrum would be handy for using its action for malleable illusions, thus saving me the action. That would be pretty sweet.
Now would a diviner Simlacrum regain portent? The spell isn't very clear on that. The Simlacrum does not regain spells, but does it regain limited use abilities? It simply doesn't say. If it does, that's every bit as fantastic as you would expect.
The Enchantment hypnotic gaze requires getting into dangerous situations, not so good for something with 1/2 a wizard's HP.
Necromancer and Evoker are both enhancing spells they cast, which a Simulacrum is fine for until it runs out of spells.
Abjurer shield can be used on others, which would be handy, but relies on spellcasting to recharge. If your DM is cool with spamming Alarm rituals to recharge, then that's an option.
An extra Transmuter's Stone would be lovely, and they are transferrable. If your Simulacrum was in danger, it could simply give you the stone and stay at the local Inn. A Transmuter Simalacrum could polymorph itself into a bird or something repeatedly and simply circle overhead until needed, it would help keep it from being a target.
Just some brainstorming.