Yes, you need it. Period.
Unless you want a craptastic program in the least desirable specialty and location, you gotta do it.
But it's not just to pad the CV. That's a piece of it, but there's more.
Clinical research puts you in touch with the attendings and residents in your desired specialty early on, and in a capacity where you can really shine unless you're a total nitwit. The value of the networking can't be overstated, and it all but guarantees an extra paragraph or two on an LOR.
You'll also show program directors in any field that you are a self starter, can work as a team, and that you can work on a project over time even when you're otherwise overworked and put out a viable product.
Finally, you may decide later on that you want a competitive field. If you have a few in mind, look for projects that overlap more than one. For now, just assume that all your other stats will be average (statistically speaking, this is true more or less), so do whatever you can to distinguish yourself.
Remember that anything you ultimately want to say about yourself must be backed up with proof. You say you want to help the underserved? Better have done some things to back this up, and not just popping in to your student clinic twice a year. Missions, volunteer, research on social determinants of health, research on the socioeconomic determinants of early readmission in your institution, outcomes of institutional projects to address these issues, etc. Whatever you want to say about yourself in the end, make sure your CV as a whole says it. Research in a given area can really help you do this.