Not all Masters are equal in terms of helping your application.
A SMP is a completely different animal from doing a traditional masters since the sole purpose of a SMP is to get you into medical school, that's why a lot of SMPs have you take classes along with MS1s, to prove that you can do the work. If you don't go on to medical school the SMP degree/certificate is largely useless since it isn't very applicable to jobs or for further education. If you are going to do a Masters to boost your application it's probably the hardest and most effective way, though not doing well (below a 3.5, or even below a 3.7) will ruin your chances even for Carib schools.
Then you have hard-science/research based masters, a traditional masters where you take upper level bio/science courses and may or may not have a bench research component to it. Although the GPA won't count as much, doing such a masters can still help by giving you research experience or showing that you can do well in upper level science classes (if that was a concern from your transcript, ie prereqs only and not a lot of upper level classes). However with research based ones it's going to be hard to accurately gauge when you'll be done, and unless you plan on doing research later those classes are largely worthless. This might be the way to go if you are unsure of how much you want to go to medical school (ie are you willing to be a 3rd time reapplicant?) and want to have some options open if it doesn't work out.
Probably the least effective in terms of boosting your application is going to be a soft-science based masters such as a MHA, MPH, or GC since you aren't really showing anything to adcoms. If you were going to spend a few years working then having such a degree could make you more marketable and have better experiences than you would otherwise, but if you are trying to go straight from the masters to medical school the only thing they'll help with is maybe clinical experience but there are cheaper and easier ways to accomplish it.
Not that I have anything against genetic counselors, I've worked with several in the past, and if I don't go to medical school and ever get tired of bench work it's something that I've thought about pursuing. It just all comes down to personal situations of what short-comings you are trying to overcome by getting a masters and the most efficient way to overcome them, and how much you are willing to risk without having a backup plan.
In regards to your question of whether it'll come across as having to no focus, I think as long as you have had previous exposure to genetics related work/research (or even if you didn't) you can frame it in the context of wanting to learn more about the field (genetic research) and thought it would help you communicate better with patients.
