I tend to be cautious with magic, since it's so easy to let a few too- powerful spells unbalance the design. However, it seems that I've fallen into the Atlantis trap, and being solely a trader or a magician is not ax workable career choice. This is bad, we must fix it. My objections to this idea seem unfounded in retrospect. Cities could produce new items from input tradegoods.
Magic is in worse shape than trade, since there it offers no way to make money directly.
Sell lead in markets. They would then have at least one useful item to produce. I don't have any good ideas for how magicians can earn money directly. Keep in mind that gold generation ideas should be limited, preferably at several points.