Spells as encumbrance

What if spells took up inventory space?

Spells must be imbued into appropriate material. Each spell has an associated "typical material".
Higher level spells require bigger or heavier materials.
A magic-user preparing spells somewhere civilized can procure materials at no cost.
When preparing spells, the magic-user must imbue the spell's material with the spell.
The material must then be brought out to cast the spell.

Other than that, no changes to the magic system.

Example: Welby the Wizard (level 1 MU) is in town, preparing for adventure.
He decides he wishes to prepare Light, which he knows and has a spell slot for.
Light requires a bundle of incense (about 1 kg) which he procures, imbues, and puts into his inventory.
In the wilderness, Welby carries the bundle of incense around. When he reaches the dungeon, he takes it out to cast the spell, rendering the incense inert.

Potential advantages :
1) I feel like it'd be really nice to have all of a character's options in the same list. Rather than flipping between a spell page and an inventory page, Welby knows he has "Light-spell Incense" written down along with, "vial of glowing poison-fungus juice".
Encouraging the use of spells for "item problems" and items for "spell problems" sounds like a good idea to me.

2) It'd also make spell-users more burdened than other classes, which I like.
A high level MU or Cleric could have an apprentice tasked with carrying all those imbued materials.

3) Flavor. I don't think I need to elaborate why it'd be cool to require incense, odd ingredients and the likes for a spell to take effect. Uh... I don't think I'd require guano for Fireball though.

4) Balancing factor. If you think Charm Person is too good and needs to be toned down, but don't want to mess with the numbers, then making its ingredient take up five times as much space as the usual spell could be an answer. If you think Ventriloquism just isn't appealing, make it use lightweight cloth in the shape of a sock puppet.

Hey wait, isn't this exactly like that old ugly concept of "spell materials"?

Hopefully not! Here are the main differences in the way I'd handle it:
1) No fetch quests. If you're in civilization, you can get the item. If you're not, you can't. No having the game devolve into guano gathering. (In my house rules at least it doesn't matter whether you can grab the material in the wilderness, anyway, because you need to be somewhere civilized to prepare spells, in any case. Wizard's lab and all that.)

2) Actually taking up space. No copper coins or weirdly shaped twigs or whatever. No, those are actual heavy items that should, hopefully, matter.

3) Focus on the spell AS the imbued item. You don't "have Fireball prepared", you carry a large piece of volcanic rock. You don't "use Hold Portal", you bring out a fitting lock and key.

4) Flexibility. If you can procure the item, and it's thematically fitting, and it takes up enough inventory space (the spell has to fit!), you can use it. An ice-based spell may use actual ice in a mountain, and night-time oasis-water in the desert.