I think having both degrees gives you an advantage in translational research and more basic science oriented research. Having the MD will give you the tools to do clinical research, but I dont think its the optimal preparation for a research career. Of course there are MDs who do all research and do it very well, but I think even they would tell you that a PhD would be helpful. You dont have to get the PhD, but the focus of training is different than for an MD and can give you the benefit of exposure to training of a "pure scientist" nature.
