Out of all the top tier glyphs, this one is underused. I often find myself converting it when playing a bloodmage.
Here is a suggestion to make it more powerful (maybe a bit much though):
With this glyph in your inventory, any time you cast a spell when you do not have enough mana, you will instead pay the difference in health equal to 1 HP per your level per mana point missing. When this happens you become corrupted and cannot benefit from health potions or healing spells (don't want to let an infinite loop with healing glyph to gain unlimited piety, or to have a net gain with a wizard).