I think there should be a few different kinds of Magus Arcana.
1. Auras. Auras are activated as swift actions, persist until a different aura is activated to replace it, and penalize adjacent opponents while providing a related benefit to the magus. For example, causing 2d6 fire damage to adjacent opponents and granting the magus fire resistance 30.
2. Boosts. Boosts are activated as swift or immediate actions and provide a significant bonus or benefit, usually based on the highest spell level the magus can cast, that only lasts for 1 round or a number of rounds equal to the Intelligence bonus of the magus. For example, spend an swift action and become hasted for a number of rounds equal to the Intelligence bonus of the magus or spend an immediate action and gain Damage Reduction 10/- for 1 round.
3. Reserves. Reserves are supernatural abilities that are powered by the magical potential of specific kind of prepared spells, usually based on school, sub-school, or descriptor. They are usable at will, usually requiring a standard action to activate, and have a power level based on the highest level spell of a particular kind of spell the magus has available to cast. For example, as long as the magus has an electricity spell of at least 2nd level available to cast, as a standard action, he can fire a 20 foot long line of electricity that causes 1d6 points of damage per level of the highest level electricity spell he has available to cast.
4. Specials. Specials are a grab bag of special abilities that alter the way the magus uses his baseline abilities. For example, they may provide sudden metamagic effects to spells, allow wands in place of spells for spell combat, provide the magus with a familiar or bonded object, allow the magus to use his Intelligence modifier in place of his Strength modifier in melee combat, etc, etc.