It is hard to earn high CPC with a multi-niche blog.
For example, An advertiser who wants to go with Display Network ad, they have better control to select the niche of the website where they want to show Ad. Any country either rich or poor (finanically) doesn't matter; they won't throw money, on a random internet site.
My suggestion would make a site about one close niche thing that interests a kind of audience. Find good keyword based on your prime niche. That should work.
If one day you write insurance, second that fitness tips, everything based on CPC checker tool. (Just saying!). Please don't expect high CPC. It's called throwing a stone in the air and wishing luck to see a miracle. That's good in dream!
If someone does not agree with my words, please feel free to leave your comments. I'd love to hear from you!