It really depends who you want to attract. I bet there are more people who like science fiction than people with strong interests in serious science and policy. But they may not be the most influential or useful people.

If you want to get attention from the best of the general public, it seems to me there are two obvious routes. One, "SIAI is in the same category as artificial intelligence research." Two, "SIAI is in the same category as public policy advocacy." Doing the first would involve talking to and winning over some academic scientists. Doing the second, which I see less discussion of, would involve packaging the project as protection against potentially dangerous technologies, and associating it with people who worry about cyberattacks, biological weapons, lab-grown epidemics, and so on.