Yes, it will look good, but like all other ECs which have been done millions of times over and over again, it will NOT SET YOU APART. It will NOT BE A GOLDEN TICKET INTO MEDICAL SCHOOL. With that said, I would only do Americorps if you are actually willing to and are passionate about doing this kind of service. It's a tremendous commitment, and definitely not for those who are looking to pad their applications. Also, if you're going in with the wrong intentions, there can be collateral damage when the needy are dependent on you. The same can be said for Teach for America, which is far worse if you don't actually care about teaching and want to pad your application. There is huge collateral damage for REAL children that are depending on you. I'm not implying that you're simply looking to pad your application, but the title of your post makes it come off this way. If people genuinely enjoy doing something, then they won't actually need to ask for approval as to whether it looks good or not, or strategically plan it.
You can add important things to your application with far less of a commitment. Hospital volunteering + non-clinical volunteering will take you just as far. You'll get into a medical school with that, and will be much happier if this isn't something you actually wanted to do. Otherwise, if you are genuinely passionate about these things, then go for it.