Doing PhD has crossed my mind as well. From reading quite a slew of articles (most of them talking about abandoning academia, few of them happen to be positive), I would cynically summarize: Do a PhD if you are either a) doing it for the prestigious degree or b) because the subject really interests you. Don't do a PhD if a) you are hoping for a tenure or b) expect to earn more. I don't think there's anything inherently "noble" in doing a PhD, so I think the outcome of the decision should entirely depend on how realistic your expectations are.
This is decent advice for many endeavours. To summarize: when choosing what to spend most of your waking hours on, don't just do it for the money, make sure it's something that interests you. Or, at least, that you can get in to.
