Mana Infusions: +400 and + 800 Mana, as abilities on branches. The wizard should have the opporunity to trade his level-up choice for a deeper mana reserve. These options should be on branches to he can skip over them and utilize the bonus later.
Instantly Learning High Level Spells: While 'getting more spellbooks' is too passive a bonus (the likelihood of spells being randomly available isn't exciting), the automatic availablity of some high-level spells would be pretty cool. For example, we could cap a branch with "Master of Wrath" that opens the spellbook and displays spells from the book 7-8 books of Wrath. You get to pick one to learn instantly. Since those high level spells are normally limited to players who customize their spell book, this should be a exciting perk to grab.
Unlimited Research Options: Right now the player is limited to 8 items. A cool mid-game upgrade would be to remove this and allow them to pick from ANY spell from their available pool, making spell research more strategic and less driven by the RNG.
Other Notes -
More Starting Mana: Wizard should start with 100-ish mana. Since this is the 'caster' sovereign, Turn 1 should be about having fun with spells, not agonizing over how to spend your limted mana resource.
No Necromancy / Dark Magic stuff: These types of abilities make more sense in the Tyrant tree.
I like the cited suggestions.
Although I would maybe change "Instantly Learning High Level Spells" to provide a recipe for instant-learning a high level spell. The recipe could tailored to a specific category of spells e.g. wrath, enhant, chaos etc. The recipe would require expensive ingredients ex. 1 radiant diamonds, 1 radiant topaz, 1 radiant emerald and 1 radiant ruby along with 50 mana. By providing recipes with expensive cost you give the player the option of choosing the specific spell or spell category from which to instant learn spells. Further with the high costs it also ensures that this is not misused.
I really like Unlimited Research Options, as I think it is natural for the Galor to choose more wisely as it is assumed Galor has superior Arcane knowlegde compared to these wanna-be wizards, who think they are One-Wizard to rule them all.... tsch, imbecile priestcommandertyrantlittlemantinker.
More Starting Mana is a natural / must for the wizard. He is the wizard and thus has focused more on arcane magic. Hence he should have built a bigger hoard of magic than any of these imbeciles wannabe wizards.
More starting spells: As a wizard you have more arcane knowledge - hence you must also have access to more starting spells. This can be balanced with weaker starting units (leaving Tanis aside). For example give him 'heal', 'haste', 'blind' or some of the other common spells. This could be 1-2 in addition to Fire Dart and Harvest spells.
Heal shards: I think as a wizard using shard-power, and shards being in the realm of arcance power, the wizard should be able to heal shards or at least do something with them. I think heal shards is also present in Priest, but I see the Priest being more about divine power/punishment. No so much about shard healing even though the Gods could heal them. Maybe move heal shards for the priest to a divine favor.
Spell of Domination: I think the wizard should have the option of casting a Spell of Winning, the same way as the tyrant, where the wizard must acquire all or a large part of the shards (depending on the map type) and win the game.
Background: Galor had an ambition of becoming the equal of Eregog. Hence he pursued arcane knowledge. He knew that Ceresa and Mithar also pursued the same goals. Fortunately he was able to defeat Ceresa, but unfortunately he did not pay much attention to Mithar. While Galor defeated Ceresa, Mithar took advantage of the chaos after the war and rose to power. After it was too late, Galor realised his error in losing track of his competitor (Mithar) and could only watch while Mithar defeated and destroyed most of the known world. Galor himself only survived through pity from the Mithar, and Galor lost most of his power. He know bide his time waiting to strike back with his revived arcane power. He becksn and crawls while he sits in his tower lab, researching old arcane magic from ancient times. He might have unearthed a tome of Eregog or maybe it is Moridan from which he develops his arcance power in order to be able to cast the ultimate spell, Spell of Domination. Spell of Domination will make the other imbecile wannabe-wizards beck to his call and whims, making him the Master of the universe world. Ha ha ha - Mithar you just wait - I will come for you.... Now bow before me, Ha ha ha ha ha........
I AM the Master of the Universe - HeMan.... dudu dum dum duuu duuu dum dum....