I second Ars Magica. Although I haven't played it personally, I've heard enough from friends to know that it seems like it would not necessarily be unsuitable for such things.
It would be workable. The magic system would have to be hacked, but that's fairly easy to do. The downtime system might need to be reworked (or it might not), depending on the kind of campaign you're running.
Yeah, hacks would be necessary, but I like the die pool approach from a narrative perspective. Players need to describe what they want to achieve in terms of the elements required. It force starts some decent story telling anyway, at least form any even half committed player. As a GM, I also tend to be up front in telling players that, generally speaking, the better they describe and story tell their actions (magic in this case), the easier I'll make those actions. RPGs are (mostly) about heroes, and I want my players trying heroic stuff, not crunching percent chances of success on their calculator watches.
The downtime system in AM is a little forced in spots, but it's an easy change. Really, we could just as easily be talking about the magic system from Mage too, since they're pretty similar in mechanics, if not description.
