You ar etalking about Masters leading to PHD. Whether you should stop your study after MAsters or continue till PHD?? Well that's depend upon your interest rather than others advice. In USA, people go for PHD for two reasons- Becasue they are keenly interested to Hold Doctorate, OR save the status after Masters if they do not get the job. Regarding money making - you might make money in other filed than doing Masters and PHD. Getting job w/ PHD may not be abundant but it is not scarce too. And the begingng salary of the PHDs could be higher than experienced MSs. It all depends upon your interest on Study and your ambition.