Point of curiosity - you say that you shut down access to guests, but when I checked who was logged in, there were guests listed - at one point 3, later 2, and recently 1.
Also, in connection with that, one would have to come in as a guest first in order to sign up!
As to the number of guests, I think it makes sense in almost any forum that there are more people who come by and read but don't actually sign up or post. And, in this case, they can still post as guests, which many have done. And, look at how many new cousins there have been lately. I'm sure they are former guests who decided to become part of the family.