Well, if earning money is the real task then I must say I kinda disagree. I had no interest in Finance niche yet I started to write about finance and made my own site as I knew it was a high paying niche. I kinda grew into the whole thing and now two of my articles are ranking high on Ezine Article's "most viewed" category and I earned a lot of money with my site (that is until it dropped for the major keywords it was ranking for).
If you want to earn money, there is no shortcut. You have got to get your act straight and try to have a professional approach. Once the cash starts to flow-in the interest and the motivation comes with it naturally. Nothing better to receive a $ check/wu at the end of every month I tell ya!