let's see, the reason for the existence for the spell slots and per day thing is that it was borrowed from vance's novels wholesale. the rational is that you have a limited amount of energy you can channel before it wears out for the day, a deep sleep is the only way to restore it. for casters, the packets of energy (daily slots) represent the maximum amount of power you can hold "at a moments notice" (wizards) "or available to you" (sorcerers/psionics) "or can channel from your connection" (divine) without losing it. the spell level thing is completely arbitrary.
you are basically describing sorcerers, but without the spell level based slots, using the alternate spell point system (in the unearthed arcana), which is the same thing psionics uses - a power point system. you have x number of points, powers / spells of different levels cost a certain number of points, spend them how you will. there are feats which allow you to burn up your health/stats for extra power points on the psionic side. the only thing that occurs to me on the magical side for "over-casting" is resetting slots via magic items, and a few other tricks.
if you reduce your casting to point based, then the only difference between psionic and magic would be the material, verbal, somatic, and focus components on the magical side as opposed to just manifesting it (and having to suppress your indicators if you want the 'think and it happens' effect).
your (A) is the same as the spellthief and psithief prestige class, as well as a few powers which steal power points and/or knowledge of powers... and maybe a spell or two that do something similar.
your (B) is the same as circle magic which is granted by a prestige class or two and a feat in... ghostwalk i think it was.
your (C) is the same as the guild-wizard prestige class, and/or a mythal or mythallar, though those latter two are epic only items.
lending power is done through the divine method of that one spell that grants the ability to spell cast one spell or so; the arcane method of a ring of spell storing, and the psionic method of bestow power which grants knowledge of a power and some power points to manifest it with.
hope that helps. i'm more familiar with psionics, personally, but feel free to ask more questions. =D