There's a great podcast called The Undifferentiated Medical Student (TUMS) that interviews a palliative care doc about what the life is like as a physician. You probably have a great idea of what that's like given your work experience, but if you're interested it's episode #21:
The Undifferentiated Medical Student
As far as advice goes, as long as you ace your remaining pre-reqs (assuming your current undergraduate gpa is solid) and do well on the MCAT you should be good as far as numbers go.
You'll need a few letters of recommendation to apply.. keep that in mind for the future while you're taking classes. Some schools need letters within "x" amount of years old. So you may need to utilize the remaining pre-reqs you have to take for this.
You'll also need a physician letter of recommendation. It sounds like you work closely with doctors in palliative care on a daily basis... maybe see if one of them will write one for you.
As one of the above posters mentioned, you probably have LOADS of clinical experience and I think what they meant to say was you may want to show a bit of humanitarianism through other types of volunteering (red cross, habitat for humanity, volunteering at a homeless shelter, something along those lines.) I was asked why I didn't volunteer (as much) in the non-clinical setting at one of my interviews (Touro - NV.) Nowhere else seemed to care. If you have the time or the opportunity presents itself to do so, give it a whirl. Otherwise I think volunteering at the free clinics you've mentioned is great.
It might not be a bad idea to get some research experience if you can. DO schools don't seem place as big an emphasis on this as MD schools, but it definitely helps to have had exposure to the area. There are certain DO schools that seem to like research a lot though (just from the reading I've done on here and some interview experiences I've had.)
Make sure you focus on conceptualization in those remaining pre-reqs! It will make the chemical and physical foundations section of the MCAT much easier to study for some exam time.
Good luck!
-NF