We all know that Invisibility is mostly a parlor trick. It doesn't really provide any mechanical bonus to any situation, other than allowing the person to stay undetected (outside of someone casting 402 or 109 and warding the invisible target). Let us not forget that most all creatures can detect you and pull you out of invisibility.

Why not actually spice it up some?

Redesign the spell to function with stalking & hiding ranks. Let it take 1/2 of your stalking & hiding ranks. So if Player A has 100 ranks S&H and hides, they'll be better hidden over Player B that has 100 ranks S&H and uses Invisibility. Stalking and hiding - you're focusing on hiding and work very hard to stay out of sight whereas being invisible, you're less interested in hiding since you already can't be seen.

Build in lores to offer functional benefits for wizards. Every 4 ranks of elemental lores gives you 1 phantom S&H rank when you cast 916.
A wizard that goes all out to have 252 ranks of elemental lores with enhancives, they'll have a phantom 63 S&H ranks - I don't see that as ground breaking by any means, but it does help them stay masked/hidden better while invisible.

Fire lore: Wizard that casts an attack spell while invisible gains crit weighting for that 1 attack and a chance to stay invisible. If pulled out of hiding, every 2 ranks EL:F gives 1% chance the magical energy of the invisibility spell will erupt, causing fire damage to all non-friendly targets in the room
If swinging a weapon
Chance to focus invisibility energy to the weapon for 1 swing that causes a greater elemental fire flare. Invisibility will fade and will need to be recast.

Air lore: Wizard that casts an attack spell while invisible gains a chance to reduce cast RT and chance to stay invisible. If pulled out of hiding, every 2 ranks EL:A gives 1% chance to immediately recast the spell at half the mana cost.
If swinging a weapon
Chance to focus invisibility energy to the weapon for 1 swing that causes a greater elemental air flare. Invisibility will fade and will need to be recast.

Water lore: Wizard that casts an attack spell while invisible gains a chance to steal mana from target and add to their mana and a chance to stay invisible. If pulled out of hiding, every 2 ranks EL:W gives 1% chance the magical energy of the invisibility spell will erupt, causing a room wide slow effect that gives all non-friendly targets 5 seconds of immediate RT.
If swinging a weapon
Chance to focus invisibility energy to the weapon for 1 swing that causes a greater elemental water flare. Invisibility will fade and will need to be recast.

Earth lore: Wizard that casts an attack spell while invisible gains damage weighting for that attack and a chance to stay invisible. If pulled from hiding, every 2 ranks EL:E gives 1% chance the magical energy of invisibility to cause a large shockwave through the ground and knocking all non-friendly targets down for 2 seconds.
If swinging a weapon
Chance to focus invisibility energy to the weapon for 1 swing that causes a greater elemental earth flare. Invisibility will fade and will need to be recast.

Activation of the spell would function similar to 520. You would INCANT 916 FIRE/AIR/WATER/EARTH for the desired lore effect you want to use.

-Drumpel