So, a tool is not a skill. I start from that when considering investments of time. When it comes to tools my time spent becoming more proficient must result in time saved squared. When it comes to skills the investment of time can result in a time deficit, because the important thing is the learning which opens new opportunities.

I learned SQL for the first time last year writing almost exclusively in stored procedures. The logic feels archaic compared with modern functional concepts but SQL joins taught me a new way of doing things.

The time invested in learning new skills becomes productive when you can use those new learnings to build new original things or make new original decisions. If you are incapable or unwilling to make/do original things learning things is probably wasting your time.