#21 - eliminate variable XP by level, return to a 1e-2e geometric XP progression where 1 XP means the same thing whatever level you are. That way PCs no longer need to be balanced against monsters of equivalent level; if magic-poor they can adventure against weaker foes and progress more slowly, or if they acquire powerful magic they can adventure against more powerful foes and progress more quickly, with either approach being inherently 'balanced'.
Edit: Stacking item bonuses on Attributes raises the problem that gauntlets of ogre power are trivial to a STR 10 PC, but very powerful to a STR 20 PC. I'd go back to a 1e style approach where items (or spells) set a flat score, probably 18 for most items/spells, and thus do not stack with inherent boosts from Wishes & stat increases by level.