If doing an MSc helps you to publish a lot, then it would be helpful. Of course, you can publish a lot without an MSc, but doing an MSc might give you more time, resources, etc. Some people even take a year off to do research if they're applying for a highly competitive specialty, but the MSc would give you a degree in the same amount of time since doing the MD/MSc is 5 years for you.
In short, if want a competitive specialty (e.g., plastics, derm), then doing the MD/MSc might be worth it if you use it productively to publish papers and other things related to the field you want. Otherwise, it's probably not worth it.