With Adsense sites I'd suggest that you probably, unless you are able to generate large traffic from high value keywords, are better off having lots of long tail keyword articles each pulling just a few visitors. There's no reason that you should not be getting Adsense clicks from niches that have a lot of interest -indeed you are better off there than in one where nobody has an interest.
I reckon that you are almost certainly looking at things from the wrong perspective.
Can I suggest that you sit yourself down and write a business plan that describes the business you want to build. List out the resources that you have, including your skills and the tools and services that you use. Draw up a plan that takes the resources that you have and uses them to build your business. At the same time identify your weaknesses, where your knowledge is weak, where your personality has a mismatch with the kind of work you need to do. Your biz plan is like a jigsaw puzzle where you fit your strengths and weaknesses into a puzzle along with the market you identify and your unique(ish) contribution to the well-being of that market.
Doing so will, if done right - objectively and honestly - help you to understand what you are currently up to.
Here's a hint though: Pages rank, sites don't.
That's really important because it goes to the heart of your question above; you don't yet understand that fundamental point about how websites and search engines work and it is obviously holding you back.
Look at what people do and how you can capitalise upon what people do. Then take the insight you gain and start work on a business. Test things for yourself, learn how to do jobs for yourself in order that you understand the constraints upon those tasks and thus upon those doing work for you.