I think the magic rule system should be randomized on worldgen. It would require extensive experimentation to figure out, and almost always lead to FUN for the fortress.
I agree, That would be fun I also liked the suggestion of each civ haveing diffrent magic. (But yeah I agree dwarf should have no magic, Besides artifacts... But ill give up the point) Of a certain character in your fort ((A mage?)) Getting courouse about diffrent fourms or playing with new spells. Angering other dwarfs and send them after him to result with a civil war... Only to be interferred with another civ following the same forms of magic running to his aid.
I also agree with some magic being given upon race, But I think what exactly that power is should be randomly genrated, Say you gen a wrold. You then go to adventure mode and play as a dwarf. Playing for a while you set fire to something. Then you notice something strange as your dwarf walks toward the fire it goes out...
For race given powers it should be subtile like that not exactly a "Ooooh all dwarfies can cast fireball!" more or less immunites leavtation, Seeing in the dark... Of course there can be diffrent sets of race abilties... Take for example [MAGIC:EARTH:INNATE] something about the earth, can range from the abilty to always find a certain stone or abilty to craft the stone to things it normally wouldn't...
On this the Innate abiltys could also have a diffrent ammount given for each race ((say elfs have three, Dwarfs five, Humans 7)) but has somewhere alogn the line of 1-10, With one being less commen two and three commen and rarer going up....