depends on you how you want to advance your character. there's nothing wrong with a full on mage. i just happen to like the diplo-type character and arcanum is great for it. as it is, you're well on your way to branching out into other magic disciplines since you are building the background stats mages need to be effective. you can, instead of picking up skills you might not want/need, just put points into other magic schools. teleport is particularly useful, especially later in the game when you're trekking all over the world and can't ride a train.
unless one of the skills appeals to you, keep leveling up mage related stats and just keep getting more spells. no probs with that. i've always liked the diplo route myself, but that's just a personal preference. also keep in mind the stats you'll have to raise to take another skill, as you'll probably be a little behind in those unless you pick something compatible with magic.
fyi, the level cap for the game is 50, and if you do most of the side quests and stuff you'll hit it pretty easily (near enough to the end of the game that you don't get bored), so you got a ways to go in picking up points.