I think you'll find differing philosophies. In general i'd go with simpler is better, and support the PhD only route. However, one could make the argument that a large element in research is intuition and understanding your system to the nth degree. If that is your research philosophy and you couple that with wanting to help and see your system on a personal and day to day basis, then by all means push for the MD/PhD.
You can also find some Physician investigators who have given up practicing completely, and the MD degree serves as a strong educational foundation on which they are researching diseases or potential advances to human medicine.
Regeneration medicine is also where my heart is, and for my specific case, the MD degree is absolutely necessary to the research I want to do. For one, learning everything you can about the human system is more than just absolutely difficult, but incomparable to the education and experience you'd receive in Med school. Further, I am a sole believer that a lot of research is intuition and being immersed in all aspects of your goal to help. For example, one of the most potent combinations in my opinion would be an oncologist or pathologist that researches cancer biology.
My opinion, wasn't necessarily asked for, but there it is..