I don't mean to belittle your idea but whats the point? You stand to gain no financial ground with a phd. I can only see this as a good idea if you want to be apart of a school your entire career.
Funny story. I know a DDS/PHD that is finishing up his accumulated 8 years of school and is trying to finish his dissertation. He has no job offers and looks so miserable every time I talk to him. He is always complaining about how he wasted 4 years + 4 more years of debt.