Should someone excited about research but who really wants to earn lots of money do a PhD?
You shouldn't do a Ph.D. if you don't love research.  You also shouldn't do a Ph.D. if you want to get rich now, since it will require a number of years living on a graduate student stipend.

However, most STEM field Ph.D. graduates have ample opportunities to make lots of money, including:


Founding a startup based on technology developed during their Ph.D., or joining somebody else's startup
Selling out, particularly if they have a solid mathematical background: there are any number of hedge funds and such that are desperately hunting for magic dust to give them an edge.
Just about any industry job will pay a well-suited Ph.D. well - not enough to make you rich, but enough to live a very comfortable life-style.


Of course, there is the danger that by the time one finishes a Ph.D., they may have become twisted such that they are no longer quite so interested in money per se, as happens to many of us.