If you are any good at writing code, trust me... you know if your code is good.

In my opinion you should go in a direction that keeps you employed and earning $$. These days this means node.js, data binding libraries like react.js, vue.js etc or go the .Net path and learn how to build MVC web sites using SQL Server.

JSON is a format for data storage and sharing. There are other formats but JSON is easily written and read using JavaScript and transported via web services. The importance of it comes from it being a "standard" that all developers know.