A few months back when I started work on the base RPG rules I decided that magic would be mana based and so magic users obviously had mana. They had stamina too, to endure some combat damage, but not as much as a fighter. Clerics on the other hand would have willpower points. These allowed them to cast divine magic, unlike the wizards magic which is arcane. So all characters would have stamina, you know to fight. Some character types would have mana and others would have willpower and some would have neither mana nor willpower.
A few iterations later I had put mana and willpower on all character classes. Albeit with greater or lesser strength depending on their class. So even a fighter would have mana and willpower. Yup, the essence of arcane and divine power in a class that is not meant to be casting spells of any type. What made me do such a thing? To practically multiclass from the get go during character generation.
The reasoning was simple. If a magic user needs stamina and hit points to endure combat. Shouldn't a fighter need mana to endure magic item use? The +2 ghoul reaper sword is magical in itself. But it is powered by the character wielding it. If your fighter doesn't have enough mana to power it up, tough luck. To use the sword the character has to level up his mana to reach the required level. Which is in itself the start of another great adventure, don't you think?
I believe this helps keep the game in control. When your character empowers magic items instead of having the magic items empower your character there can't be an power escalating effect that breaks the game. A game mechanics meltdown so to speak. It is the character who sets the caps on what can and can't be done.