I agree with watson. I didn't get in anywhere last year and I'm applying to work with some of the same POIs this year (I was waitlisted at these schools last year). When I emailed my POIs, I never mentioned that I'm reapplying, I just stated that I was interested in their work on "blah blah blah" and asked if they were planning on taking students. Like watson said, I didn't want the knowledge that I had applied there in the past to potentially bias my current application (not to mention that it would have been awkward to write).
As far as mentioning that you are taking master's classes, if you are only taking classes and don't intend to get the degree, then I wouldn't mention it in your email. You can mention it in your SOP later on, but in your email I would just keep it simple and to the point. However, if you do almost have your degree, you could mention it very quickly. I basically said, "hi my name is psychdork, I'm currently finishing my master's degree in psych and am interested in your work...". I don't know what other people think but my reasoning is if you are just taking classes then that might come across as indecisive...which you can explain in your SOP but would take up too much room in your email.