Acquiring New Arcane Spells

I've sort of left out any discussion of how Magic-Users, Bards, Elves and Gnomes get additional spells into their spell books.  Of course, they can copy them from captured spell books or scrolls if they have Read Magic (which they all do, unless they do something really stupid). 


However, I never made up my mind about the process of gaining spells in other fashions.  I believe the Old School method was you just had to find them and copy them.   ACKS allowed you to do research at library, but the mechanism is all tied up with the Repertoire system they use.  


Various Newer School versions of the game have your mentor teach you exactly 1 spell each time you go up a level, until a certain level and then stop.  ACKS I believe granted 1 spell per level through your own efforts.  


Almost every version of D&D discourages characters and NPC's from sharing spells willy-nilly with each other, but doesn't have a scheme to enforce this.


I'm really torn about the whole business.  At one level, I'd really prefer to require that all spells be captured from a spell book or scroll.  However, that might totally gimp mages if things go pear-shaped. 


Perhaps we could rule that when a magic-user goes up a level he gains a random spell at his highest spell level, or perhaps he picks 4 spells of any level he could cast and gets to draw randomly from those four.  Now, that's why I do Dr. Skull's Workshop.   Writing stuff down does help sort things out and brings some good ideas to the surface.


So here's the proposal:


1--Every Time an arcane caster goes up an experience level, he lists 4 spells that he is interested in acquiring, and these spells can be of any spell level that he is able to cast.   The DM then rolls randomly among the 4 spells and the resulting spell is added to the caster's spell book (requiring one dose of magic ink).


2--.  Once a magician is beyond the apprentice stage, he can add a spell to his book either through his own discoveries when he gains a level, (see entry 1 above)  or when he does research to create a new spell, or by copying a scroll spell into his book (destroying the scroll in the process), or by copying from a captured spell book, wiping the spell from the original book.  In order for two magicians to trade spells without losing the spell from his original book, each must make a scroll and trade the scrolls. 


3--Rules for Travelling Spell Books: are changed, the spells in the Traveling Spell Book are written in them using the rules for making Scrolls, not for copying spells into a book.


I like this a lot now.   This keeps all the enemy spells books from becoming proliferating monsters.   You copy the good spells, and sell off the partially empty book.