I've long been in favor of scaling the Sorcerer's HP recovery by level - something like (level / 2) HP per MP spent would be a slight buff overall, making him less of an early game behemoth but stronger later on. (Currently he always gets 2 HP per MP; this would give him .5 HP per MP at level 1, 2.5 HP per MP at level 5, and 5 HP per MP at level 10.) I don't think his other abilities warrant changing; Mana Shield is a very strong ability as is, essentially being equivalent to +20% bonus damage, and excellent against monsters with phys resist or death protection.
Wizards would be quite tricky to modify. As Avatar pointed out, -2 MP cost would make PISORF just ridiculously overpowered. (Although it wouldn't benefit from the Crystal Ball anymore, since as I recall you only get a charge when casting a spell that costs 3 MP or more.) Honestly it's overpowered even at 3 MP; the only thing keeping PISORF Wizards from easily ripping apart all but a couple of dungeons is that it's one of the most time- and scumming-intensive strategies in the game.
On the other hand, applying MP cost reduction only to expensive glyphs would overall be a huge nerf to every strategy other than pure fireballs. All of the other expensive glyphs are pretty bad choices for the WIzard due to his damage penalty (and lack of any other advantages): CYDSTEPP and WEYTWUT both favor heavy hitters, APHEELSIK is generally only useful if you already have a good regen game, which the Wizard lacks, and it's not even good for fireball strategies anymore because it lacks synergy with BLUDTOPOWA. Wizards have long favored the cheap glyphs.
I doubt there are any minor tweaks that would significantly improve the Wizard without introducing major balance problems of their own. One more significant change that would be interesting and potentially a lot easier to balance (and which would encourage using a more diverse set of glyphs) might be to remove his MP cost reduction but have him use glyphs more effectively; the Wizard could get the same perks with CYDSTEPP, HALPMEH, and APHEELSIK that the third tier classes get, and similar perks with other glyphs, e.g. +40% damage and 4% resist reduction from BICEPS, +10% dodge from GETINDARE, +30% resist from ENDISWAL, etc.