I was rereading the first edition Advanced Dungeons & Dragons Player's Guide and was comparing it with both OSRIC and the Labyrinth Lord Advanced Edition Companion and something struck me. Intelligence dictates how many spells a magic-user can learn (the chart for this is identical between OSRIC and the PH, but not the AEC). I got to thinking about how limited MUs were and yet they had such an abundance of spells to select from (many more than the other 3 classes). Something I have never liked is how willy-nilly spell learning is in AD&D, though that was fixed, to a point, in Dragon 216 with path magic. But that still didn't completely fill the void I was seeing- casters who could concentrate their learning and become powerful within a niche. The light bulb struck and so now I have an idea to fix that. Something that works for both editions of AD&D plus a variety of OSR games.

Magic-users (and illusionists in 1e) can learn a spell multiple times, but each time it is if a new spell is learned. For example, a magic-user with an intelligence of 16 can learn 11 spells of each level. If they wanted to concentrate on Shield, they could learn it two or more times. If the character learns it four times (the initial and three enhancements), then they can only have seven slots left for other spells. Only one enhancement can be learned per level. Some DMs may require the use of the spell design rules and others just a lost of the slot (which is brutal to casters with lower intelligence). And the number of enhancements allowed for a single spell is up to the DM.

The enhancements are what are to be expected- a one size increase in the damage die, a 25% boost to range, area of effect or duration, -2 to saves to resist the spell and finer control. Though there are not many spells that require a die roll (such as Teleport and Reincarnation), finer control allows the caster to roll twice and pick the more desired outcome. If the DM allows, some enhancements may be taken multiple times.

Here are some things to keep in mind. These rules are simple and do allow a player to get better spells in low level slots, but they also reduce their flexibility and may bite them in the rear if they need a specific spell to deal with some threat. It also may put them into a corner if they enhance spells that are useless in some situations, like the fire mage who is part of invasion of a fire giant castle. So they are not a panacea, but they do allow for certain play styles.