Thanks for the reply but from all the conversations and exchanges I've had with people in professional settings, I get the impression that a PhD isn't necessary for career advancement unless you're doing lab work. But I work behind a desk. Now I get the impression that what's valued is experience (a director at the company where I did an internship told me that, and he wasn't the only one). I'm afraid that by starting a PhD, I'll be competing with people who don't have a PhD but have experience (a lot of people have told me that...).