Time to answer my own question after all.
I counted yesterday and was surprised to learn that my main save only has five haunted houses at the moment. I could have sworn half of my Newcrest consisted of those, but nope, only two of them are in Newcrest, the others in Glimmerbrook, Mt. Komorebi, and the island of Windenburg. There is one additional haunted house in my second save that I started a little while ago, adding up to a total of six.
But number seven is already on its way. I'm planning on building the ultimate horror house on Sulani, one that isn't just haunted by spectres, but also regular ghosts and island spirits, and situated close to Mount Magma. Fun, fun, fun! :D
