It needs only 6 new members to reach the critical threshold of 300. I think current members of the section are more open to mathematical sociology than most other sections. Furthermore, the topics are interesting and important. See the section mission statement here and a newsletter here.
Speaking of ASA sections, Jeremy posted some interesting data the other day: The percentage of each section which are students. In Mathematical sociology it is one quarter, which is lower than average.
Philip Cohen also had an interesting post a while ago about gender differences among sociologists where he graphs section membership by gender.