(solemnly)
When I was first starting in the game, everyone around me was doing over the top things, and I was the conservative kid arguing for moderation. I kid you not.
Now, 30 years later, everyone around me my age argues for moderation, and I'm the one gunning for the over the top conceptions.
I suppose the long War Against the Wizard, which I had the misfortune to have to watch, caused me to take a more extreme position, irritated me into revolt and rebellion, and otherwise cemented my position as an advocate for high powered wizards.
In a sea of Nerfing, there needs to be at least one lone voice out there, arguing the case for power and extremity, a bit of the uproarious times of long past in his voice.
That would be me, I guess. (sighs)
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Incidentally, that was how wizards in my game obtained spells: through scrolls and books found through adventuring, and through proving themselves to a mentor or college (through adventuring) or as a reward from a ruler (for adventuring.)
Of course, if a PC wizard and another PC wizard wanted to swap spells, that was fine with me. The usual rules for learning spells, maximum spells knowable per level, and the time and money required to inscribe spells were all in force, of course (not to mention the limited capacity of spellbooks.) And - to quote yourself - superior players cooperated, and their PCs did swap spells, and this was a prime way of obtaining those priceless spells.
You can create magic items in my game. The 3rd edition rules allow for it.
However, I use the item destruction rules from 1st and 2nd edition. So when that Fireball comes, and you fail your save, all those magic items must save too. If even one fails, it bursts into magical flame, and all your magical items must save again.
Those low level magic items are probably not going to be a match for a Fireball (magic items made by powerful NPCs that you found in the wilderness adventuring will be Fireball resistant.)
You have probably lost all those minor magical items you made, from that Fireball. You failed your save. A pity. I the DM shall cry hearty crocodile tears for you.
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For the aspiring archmage ...
Consider the Shapechange spell as I described it. No archmage (or anyone else) who has this spell will share it, with a stranger, for any price. Why share the secret of such awesome power? Ditto for those other spells I described.
So, if the aspiring wizard wants these spells, all she need do is to take them by force from the archmages in question. That shouldn't be too difficult to do ... no biggie at all ... (chuckles)