I also don't vaccinate. However, I do feed medicated feed. I've gotten away with out it, and they do fine if exposed early, but cocci is a very high risk in our soils because it is damp year round which is perfect for the protozoa to survive. Warm damp humid areas can be even worse with cocci. Living in the middle of arizona... it might not be so big of a deal. Often they can build up a great immune system without medicated feeds, just give them early access to soil, like within the first week, so they can build immunity up. The med for cocci just prevents the protozoa from reproducing, so it isn't actively killing anything. That means if cocci is so high in your soil, they can still get it.
As for mericks. It isn't really a risk here so I don't do that one either. If your flock has a history, or if the area you are in has a high risk, then it can be a good idea. Different places, different ways really.