The key qualities you need to succeed in your dissertation is a capacity to persist for a very long period of time on difficult problems - difficult not only technically but conceptually. One of the key skills is to learn how to formulate what is even the problem to solve. 90% of a PhD is just supreme stubbornness in the face of adversity.
If you genuinely enjoy it and are willing to forego a salary for 4-6 years (the average time it takes to finish a PhD in the US/Canada is 6 years), the average PhD stipend is about 20-25k - it's a very exclusive experience and people will always give you a default amount of deference on most matters if you don't care for modesty.
But if you just want a boost to your career or like Dr. in front of your name I advice against it. Generally speaking a PhD is always a net-negative for personal wealth creation.
The goal isn't wealth creation or to boost my career. The desire comes from two things: 1/ Physics has always interested me, I am willing to do deeper, good at Maths (calculus and all), and I regretted not pursuing this more thoroughly (and abandoning it) during my undergrad. So, kind of want to finish it off. 2/ I am looking for a permanent switch from business to other fields. Not to do with money so much, more to do with working on things I like.
I recognize the faculty positions would be limited and ultra competitive. I envisaged becoming a part of those research labs (provided everything works out), or join someone as a postdoc fellow / Research Scholar. (Money is not the objective here). A Phd helps because my knowledge at this point is more theoretical and just because of what I read. Your perspective on Phd helps, many thanks for that too. (I have had many others say the same thing :) . So I know it will be tough.)
If you don't mind me asking, where did you end up when you say you went into industry?
A wise woman I met said to me when she was around 60 that she should go to university again as she likes the good boost to critical thinking. She ought to do that in every 10-15 year and it's about time. I'd say it's a nice example to follow.
If you are set on a permanent research position at least in the US lab system those are in my experience even more competitive than faculty positions as they come with the luxury of not having to teach. A post-doctoral position is quite possible but you have to consider you will like be early 40's by the time you finish and competing against late twenties, early 30's and post-docs are typically renewed at 3-4 years and are not permanent positions either, depending on the school and country they may not qualify for the same benefits in the university system.
By all means you should do what you feel, you are talking to a guy who left his job and now spends his time trying to develop a video game so I know a thing or two about jumping off the veranda - sometimes you just take a leap of faith and see what happens.
Conversely you could always “master out” of a PhD program if that’s what fits/a possibility but again you haven’t mentioned anything like “I want to be a professor/do research at a national lab” etc
Certainly not trying to dissuade you from anything and I find your post inspiring. Best of luck and hope you find what you’re looking for
Edit: kind of went on a tangent rather than focusing on the original question. If financials are not a huge part of the question I think your profile would make for a good graduate student. There is precedence for success among people I’ve known with similar age/educational profiles. If ones’ goal is to become a faculty member that’s more subject to chance