First of all: yes, some of my arguments where far-fetched. That's why I made the overweight statement at the end ;)
But I think there is some confusion. With item I mean everything you can carry. So item = staff, spellbook, shovel, snowball, shield... Also I taught to attach only a few spells to one specific item. Like you have the "staff of time" which can only be used for fasten time, slow time and stop time. So to use other spells you need another item. That means also that not the player choose the spells he want to use with this object, but the person who designs it.
Another thing I did not explained clearly is the power-up. I imagined like two kinds of usage. The first is click only, you aim and click, as you do it with the bow at the moment. When you hold the button only a short time, the arrow will fly only a short distance, when you hold it longer, it will fly longer. The other is for things you want to do fast, and maybe which need more than only one x and one y position. Think the frostbolt scroll, at the moment it has only one strength, so when using it you just have to choose a direction. Now imagine you click, but hold the button, move your pointer a short way and let it go, in the second you let go your mousebutton it will be shot - with a strength depending on the length of the way you moved. So there is no time-component. Or, as a example which combines both, imagine the wind scroll. When you use it now you can only chose the direction it will go. When using the mouse you can set the start and the end and so the place and the length of the wind, here powering as in the click-only way could be possible.

But, when you look at my so called "magic system" honestly, and cancel the words "staff", "spell", "mana", "magic" and so on, there remains nothing more than the idea of using objects/items more with the mouse and power up certain effects.