I think that what I see in the images, especially #2 is the result of using layers and masking to "paint" in a more saturated sky. For most of these images, it would be a thankless task ... given all of the branches. For the second image, it would work better with a softer brush, i.e. larger diameter and much lower opacity at the transition between sky and trees. My Skagway, Alaska image (thread title: "the only blue box in town ...") is an example of using layers and masking to apply a sky layer with lower exposure and a custom gamma curve.