If you don't have high creativity, then this is pretty much just a waste if them, but writing a novel can net you anywhere from 2000 to 3500 or so simoleans from what I have seen, that's quite the useful chunk of change.
Unfortunately, writing novels aren't as rewarding as painting and seem to take forever. It takes about 27 hours to write a novel, and it seems that prices do not grow with additional practice past maximum creativity, unlike paintings.
(Meu eu simulado estava escrevendo um romance há séculos e não terminava. Agora eu sei porquê.)