That sounds valid! I mean, it would be a bit busted combining Arcing Juice with Searing Juice for something that's equal to Silver Bullets for everything, but maybe there could be thematic guns that auto-convert "Basic" Juice Ammo into special Ammo, just like some weapons in the hit 2-d survival game known as Terraria or something similar. I was also thinking the same idea with the whole "Chewing up inventory space" thing, except maybe make it so that Juice Ammo would be more common than normal Crafting Juice, and has the ability to stack, maybe also allow it to be altered by some Crafting Juice for various effects.
But yea, I personally like it! I wonder what Fish thinks...