How about something that lowers population, but increases society level? "Rapid Society Development: Pump resources into rapidly developing technology for this society's planet, however many people refuse to move with the changes and will abandon the planet for a simpler life." That way if you're willing to endure a bit of hardship now, you can get to the society level you want sooner. The only problem might be integrating this with the current system of upgrades to stop abuse.
i'd rather have something that kills soc level....
