The irony here is that a "saving throw" generally means an all-or-nothing system, whereas "resistance" tends to be a proportional reduction to damage. A saving throw system is actually what we do have, whereas an actual magic resistance is what you're asking for.
i guess i was thinking more of the D&D system where a successful reflex save means you take half damage or so forth. and also, everyone has some reflex save worth mentioning, whereas (correct me if i'm wrong) only characters with good INT currently have spell resistance?
when you figure in monster abilities and morale effects, there are actually quite a lot of opportunites for saving throws in this game. i think they'd do better axing magic resistance and going for classic D&D will, reflex and fortitude saves based on wisdom, dexterity and con respectively.