If its going to be a suicide pill, I say we don't allow magic at all, as it would be pretty pointless. I can't really speak for everyone else, but in my experience, I've never really seen magic break an RP or NRP.

Even in the highest fantasy setting, you rarely have a mage capable of leveling a continent, as appose to most Sci-fi Rp's where you have the ability to wipe out whole systems. (or at the very least knock a meteor onto a path with a planet)

There's only three things you really need to restrict with magic; 

Reviving the dead (not really to be confused with raising the did with necromancy per-say but that's another monster in of itself),
Teleportation 
And time manipulation.
(And we can add insta kills from a distance against PC rulers cause some guy sacrificed to NPC peasants) 

Aside from that, it's important to have a bases, the main fear with magic is the fact it has no easy scale. Which usually means you have to compare it to another well known establish universe. I usually favor Conan level personally, simply because it takes forever to cast anything and requires expensive regents to use. 

But really, the main fear with magic is that people think someone is going to pull a meteor or some nonsense from the sky and nuke their city, which really I don't see to many players doing, as most are dead afraid of stepping over the line as it is, and anyone willing to go that far probably shouldn't be in a NRP in the first place. Aside from knowing exactly what you can or can't do with magic in a setting, really common sense is the best way to go about it. 

At least that's my two cents on the matter. :K