I am an RD and will get my MS in Nutrition next month. I also found out this week that I will start PA school in Jan 2016. I think it has been very beneficial so far, but not in all aspects. There are many pros/cons just depends what schools you are applying to and what they consider quality of HCE. Unfortunately, few (even many) schools do not appreciate or understand the knowledge background of an RD.
Some schools give priority/bonus points if you are a credentialed practitioner. I have saved a good bit of $ to put toward tuition, but that's only because I have no loans. I do not regret becoming an RD first. I always knew that I wanted to be a PA, but getting in is so competitive these days, I did not want to be stuck working as a med assistant for more than 2 years taking blood pressure/refilling meds day in and day out. If you are an RD you will always have a career to fall back on no matter what.