Formerly known as a dangerous area filled with day laborers, the old Sanya is slowly dissappearing. In its place are westerners who are trying to save as much money possible in expensive Japan and young people who do not even know that the area is known as "Sanya".
I have heard other countries like the USA get very negative when they hear former blue collar areas (such as where Ford Plants used to be) are disappearing. For a country that is supposedly much less welcoming of immigrants, notice how little Japanese think of dissappearing areas such as Sanya. It is even taken as a positive thing. Perhaps there is a different interpretation of "change" among the cultures.