I've thought about going back to school to get a Mechanical Engineering degree, or Chemical Engineering degree.
I grew up with my father being a machinist, and eventually going on to being a QA specialist for a large defense contractor, so I've be lucky enough to be able to learn a lot when it comes to machining and designing. Spitting out a 3D design from a printer is really cool, but nothing beats slapping a chunk of steel into a Bridgeport and ending up with a precisely-milled widget.
My wife is also an engineer at one of the largest (probably largest) physical testing companies in the world, and got her Chemical Engineering degree as well. There's constantly stuff she's telling me about, problems at work, custom things she's doing, and we get pretty deep into conversation sometimes about how to best solve the problems.
The money just isn't there compared to being a software engineer, but like a lot of people have said in this thread, maybe this is just a "grass is greener" thing: these problems that I can't work on just seem that more tantalizing than being the person who is actually dealing with a backlog of them. Vacationing in other people's jobs is fun and easy, and ignores actually being that employee.