Thanks for this. I'm especially interested in the intersection of gene-environment interactions/environmental health, chronic disease epidemiology, and health policy. After my MPH, how much potential is there to get involved in these sorts of fields/projects as a medical student?
Since you are pursuing the degree out of interest, I'd say there's a lot of value for you. The cost is an issue, as grad school is ridic expensive, and there are opportunities to get it paid for later in medical training.
That said, I fall more in line with
@LizzyM s thinking. If you just do the bare minimum to get the diploma it's probably not so impressive. If you make the most of your time, you can really get some valuable experiences. I'm finishing my MPH in Epidemiology now (worked fulltime while doing it). No regrets.
Cool things I've gotten to do while getting my degree:
volunteer at the student run free clinic for a couple years with the med, nursing, pt, dental, and pharm students
finagle my way into working on a cool clinical trial at my job that wasn't really a research job
do my field experience in the ED of a busy county hospital doing informed consent, data collection, patient interviews, and chart reviews for clinical research projects (also got a ton more shadowing in at same time)
serve as a grant reviewer for Ryan White HIV/AIDS program grants
student run ID journal club
network with cool docs to shadow and have as mentors
Masters thesis/research project
Learned a ton, much better critical thinker for it (made me look really good at my unrelated job)
So... I think I almost got my money's worth (tuition being ridiculous and all)
As for your second question, in med school it will be somewhat school dependent, but at a large academic medical center with a school of public health you should be able to participate in those interests.