on two of my entry steps, I have a small chip on the edge. They are about finger tip size and are through the plaster so the chips look dark. Will such chips continue to degrade and thus grow if not repaired? And is repair a simple DIY effort?
Depending on the age and condition of your plaster the chips may stay the same for 10 years or start chipping off tomorrow. If you have old plaster that is starting to de-laminate from the gunite it could be a problem.
If you have the skills the time and the money you can do this yourself. The tough part is matching the colors. That is the number one reason to hire someone it to make sure its done correctly and matches.