I think it may be a combination of two contributing factors. One, as TressesOfNephthys said, it may be that we are more sensitive to the paranormal during the cycle of the full moon and I do believe that it is also a possibility that spirits are indeed more active during this cycle as well.
It's no secret that the full moon has a profound effect on not just the ocean's tides, but on people as well. It's a well known fact that law enforcement officers dread the cycle of the full moon because of the effect it has on the public in general. Have you ever noticed that people tend to get a little weird during a full moon? They tend to be more uptight, hostile and aggressive, or they go the other way and become more sensitive, sentimental and emotional, all depending on the personality of the individual. For a woman, most will find that their PMS will be even more intense if it occurs during the cycle of the full moon. The moons gravitational pull effects the tides and everything living so in my mind it also stands to reason that it likely would also have a direct effect on spirits as well.
As for your dogs and why they didn't react to the apparitions you sensed, one explanation may be that they sensed no danger to you or themselves. Animals are well known to be highly sensitive to the paranormal. I personally believe that a lot of the reason for this is that animals, unlike humans are not told from a young age, "There's no such thing as ghosts" therefore their minds remain open to the paranormal where as children, most humans are conditioned from an early age to close our minds to such possibilities. Point is, not only can animals readily sense and often times visually see paranormal entities, but they can also sense an apparition's intentions for either good or evil. Your dogs sensed no danger, therefore they didn't react. I'm betting that you also sensed no threat or danger from these spirits, otherwise I imagine your post to this thread would have been quite different. Trust your instincts and the instincts of your pets when it comes to spirits. If the hair on the back of your neck raises up and you get an unexplainable sense that there is something malicious or dangerous in your presence, don't ever ignore that feeling, trust your instincts, they were developed through the process of evolution over thousands of years for a reason, to keep you safe.
Hope this helped.