You could have a whole range of potions/essence/liquids/powders which drop from monsters and are all required to make the potions to use in casting a particular spell.
For example, collect glittering dust (existing), troll blood and tengu sweat to make a particular spell. Mixing these in a combination/quantity of your choice would make the spell have different strengths/be more or less powerful in the spectrum of possible effects.
Not only would it add more variety to the spells (if ever it were needed) but the spells would be variable in power and effect, depending on the casters pre-determined choice.
I for one would find it interesting to spend a little time mixing stuff and making my own potions.
How would it work? Each potion would have a template by default that would have w, x, y and z effect. By mixing items 1, 2, 3 and 4 in certain quantities and order, you could make w, x, y or z be stronger/weaker/equally strong.
Let's take a healing potion....
W, X, Y and Z could be healing, divine favor, protection and smiting. If you added more crushed avicara teeth than putrid ettin skin, you could boost the protection in that potion. If you added drake saliva to the potion, you could boost the healing too.
So, how would you actually cast the potion? Just like scrolls of hero's insight etc. Double click in your inventory would make all your spells have this added effect for a certain time or even be instantly applied to the whole team or just the immediate area (like balthazars aura).
So if i had a potion that boosted the healing and i used it at the same time as using a healing potion, the healing would be boosted (just like divine favor does).
If i had a smiting and protection potion and i used this, i could reduce the damage taken on allies while also smiting the nearby enemies.
There are so many ways in which you could use this system, it just boggles the mind to think about it.
Ebon arrow potions (arrows of all allies have earth damage for X minutes).
Firey blade potions (all melee allies deal "additional" fire damage).
Potion of strength (all allies skills are boosted by X% for X minutes)
So many possibilities and a great gold sink. Great to get new items dropping too.
I'm sure everyone would love to mix their own spells.
Maybe it could pave the way for a whole new breed of classes?
Afterthought... Maybe several people using different spells would end in conflict between the two spells. Maybe they could be applied to the caster only? Anyway, the idea template is there.
I don't know if this idea exists elsewhere on the Net so please don't scream EQ,D2...because i've never played them, THANKS!

Thought on this?
EDIT - Sorry Mods, should have been in Sardalec.