Long story short first: I'm not a developer, yet I've built a Wordpress development digital agency that now has 5 full-time freelance developers and repeat clients from 9+ countries.
Some of my thoughts:
There are people that can set up Wordpress, install a theme and couple of plugins and sell that as a service. Such a service has a very small value though, high competition hence very limited yield.
There are people that can not only set up Wordpress, install a theme and couple of plugins, but also make tweaks to the theme. This requires front-end coding skills, which can easily be learned for free by taking some awesome courses, example: codeacademy. Demand for front-end developers in Wordpress area is huge and even though there is a large competition, there is a large demand, so yields are pretty good.
Next level is Wordpress back-end development, this requires knowledge of PHP, SQL and JS/Jquery. The value you can provide with such knowledge is the ability to custom code plugins or custom fields, integrate site with 3rd party APIs etc... Being able to provide this service makes pretty much anyone "always busy" with clients in pipeline.
My agency provides all three types of service I mentioned, yet I am not a developer myself. How did I do this? I hired developers and found clients. My value in the package is the ability to sell value to a client, translate client requirements into an effective project plan and effectively use agile project methodology in working together with the developers to deliver the project and make the client come back with more projects.
If you're interested in learning more about what tools, methodologies I used to build my agency, hit me up.