B/X Wizard and Elf Spell Lists

As JB from BX BlackRazor has pointed out before:

Magic-users and elves are limited to the number of spells they may know, and their books will contain spells equal to the number and level of spells the caster can use in a single day (thus, the books of a 4th level elf will contain two first and two second level spells).

I have not been playing this way in my B/X games so far. I've been playing that characters can learn spells from spellbooks and scrolls that they find and scribe them into their spell books. I haven't really put a limit on the spells that a wizard/elf can have in their books. Each day they have to memorize spells from their spellbooks. This is pretty close to the way I played 1e and 2e AD&D. I hardly ever worried about how many spells a PC would learn.

However, I've been thinking of loosely following the rule from the expert book listed above. But I would like to alter it in an interesting way:

Wizards/Elves would only be able to "learn" the number of spells equal to the number that they can use in a single day.

However, they can keep spell books with any number of spells in them and they can learn spells from the spellbook of an enemy, but if they already have learned the maximum number of spells of that level they must trade one spell for one spell (essentially learning the new spell causes them to "forget" a spell that was already in their head). It takes them ~1 week of uninterrupted study to change a learned spell slot. Wizards could change spells on the road but only if they don't engage in combat, take damage, or face harsh weather conditions, etc... anything that could take a large portion of their concentration off imprinting the spell into their mind.

Wizards/Elves would not need to consult their books to memorize their spells each day, instead they can cast any of their learned spells up to the # of spells per level that they may cast per day. This would remove the need for wizards and elves to bring spellbooks along for the adventuring trip (unless they think they might want to change a learned slot on the road). If a 2nd level magic user has the ability to learn and cast 2 spells per day and has Magic Missile and Sleep learned he could cast one of those each in a day or cast two sleep spells in a row.

Using this method would improve magic user and elf versatility, trading it for an increased limitation on the amount of spells they can have access to at any given time. Also, having access to another wizards spell books would allow you to "learn" more spells and transcribe them into your books - so there would still be a good reason to have wizard mentors and guilds. I'm not 100% convinced I'd like to adopt it, but I may give it a trial run this fall if I can get together a skype game with the Castle Amber crew. I talked to them about continuing more of a campaign following up on the Castle Amber adventure with a couple of others that I have.

I think I'm going to run them through the Master of the Desert Nomads followed by the Temple of Death adventure. I think those two adventures should easily take 4-5 decent sessions each and would likely bring all of the party members up to 9-10th level if they can defeat the modules.