I would say this is more of an issue of letting your job define you.

I work in a highly specialized segment too. There is maybe 100 people in the world that do what I do. And there are maybe a dozen places in the country to do it and the jobs are few if you want to move around. But being so rare, I also know that a few phone calls can land me a new job tomorrow if I needed it.

I took get bored and feel confined. My job is important, but I don't get to explore as many concepts and after a few years, the rate of learning new things has slowed in my career. There is less easy to access learning and much more hard to access learning that must be done by being the first explorer of the topic.

The way I have balanced that is not starting another career. The next one would eventually hit the same plateau. I don't want a career a decade. I am good at what I do and use it to make an excess of funds. This is the best for the economy and the economy rewards me for doing it.

The way I handle this issue is the yearly project. One year it was programming my own thermostat. Simple enough until you add in multiple temperature points, automatic dampening, and logic to detect a phone and optimize heat levels based on occupancy. It was a fund lesson in control systems.

The next year it was welding. Welded snowblades for a lawnmower, a bunch of furniture frames (my coffee tables are a bit overbuilt), and some sweet aluminum art.

This year I am using a small forge and lathe and going from scrap aluminum to sterling engine.

You don't have to be confined to exploration in your job. With a solid engineering background, wikipedia, libraries, and the craftsman that live around you are huge resources to learn and do all kinds of wonderful things.