I am planning on doing a PhD because of financial benefits in the long run. Here's why:
- Immediate respect. It is harder to question the authority of a (technical) PhD. This is much more pronounced in 3rd world economies. Also Germany. Basically anywhere besides the non-super-meritocratic US. This is a huge benefit: my opinions are more likely to be listened to, my consulting fees are likely to be higher and be more credible, career breaks (maternity) will not set me back by much, because a PhD proves technical mastery of an area as well as tenacity, responsibility, and independence - all of which non-PhDs will continously try to prove to new coworkers and new management.
- Universities are forever open, but not so with Masters. That gives immense job security as a private university lecturer for the rest of your life, in any country (flexibility to travel and find a job even in countries you don't speak the language of). Private universities in rich countries pay a lot to be able to say they have a, say, MIT-PhD on their faculty. I knew a person who had a data-entry job and saw the faculty salaries in Saudi Arabia. The profs were making 396$k/year, housing and living costs fully compensated by the university.
- Flexibility to find jobs forever (especially because of the university thing). Normally I imagine it would be harder to be a salaried employee after 65 years of age. Nobody will hire you because it is so weird to have an employee your dad's age. Ageism is real. But because you can always lecture, you are pretty much unretirable.
The 4-5 year salary cut is nothing compared to a lifetime of these benefits and zero anxiety about job prospects after 50. I personally want to work and earn money in a respectable job well into my 80s.