This was and still is the best guidance[1] I ever indirectly received in uni. I hope it continues to help others.
NOT… A way to make more money
While we haven't heard any statistics for the past couple of years, graduate students used to estimate the ``payoff'' using the starting salaries of Ph.D. and M.S. positions, the average time required to obtain a Ph.D., the value of stock options, and current return on investments. For a period of at least five years that we know, the payoff was clearly negative. Suffice it to say that one must choose research because one loves it; a Ph.D. is not the optimum road to wealth.
The problem is that today the more likely outcome (there are exceptions, some of them posting in this thread) is that one has wasted 5+ years in, at best, advancing someone else's career.
"I love research" is too often a way for institutions and professors to exploit the young.