Self publishing causes a huge increase in noise since there are no barriers to getting published. So there's a big risk you'll pick up some garbage, but also vast supply which drives down prices. It also means new books on popular subjects can be quickly written, so unless you have some credentials the odds are stacked against you. So i think it comes down to marketing one way or another.

I plan to write a book one day, but mainly as an aid to establishing my credibility for courses I'll run, so marketing from the other direction.