Give up being an engineer, go back to college, and do something else?

In this rough economy, should people go back to college to get more 'job' training to strength their degree? I have a masters in engineer and, for five years, I looked for an engineering job in my field and the closest I came to it was designing air conditioning systems for buildings. I asked a former college professor about getting a PhD. He told me a PhD is only good for teaching college. He recommended to me that I get a degree in economics or education instead. So, I'm asking you is there anything I can do to build on the my current degree? I'm 33 years old and by the time I get something else, I would be around 36 or 37. Would my age and years out of the work force deter me from getting a job?