This is one of the few things that used to irritate me about GalCiv. These days, I just live with it, but...
It seems like if you have a world that doesn't have any more social projects to build, you could at least select something like "Luxury Goods" or "Consumer Goods" or whatever you want to call it, and recapture some of the "lost" money on that world (like, 25 or 50%). But Brad is against it, saying not that it would be too hard on the AI programming, but that it would be too hard on the actual programmers. I don't understand why... you'd just add back the fraction that world's social cost back to the player balance during the production/resolution phase.
Having individual slider rates by GOVERNOR would allow for some complexity... you could set one of your governors to 0 social, for instance, and just swap that world over back to your infrastructure Governor. But if you get that out of SD, they might as well just allow individual world slider settings, as it isn't only one more step to allow users to do what they think they want to.
Having individual sliders would be very nice... so you could tell those little worlds to just not make any military (Military to 0) or those late game worlds to set their Social to 0. That wouldn't be a big deal from the AI's point of view. It would actually let the AI be more efficent then the Human. However, as many of us would want to maximize our own side, it would add to the micromanagement of the game for us, and that would slow down the game and our fun. And Constructors are bad enough as it is.
Maybe in a future GalCiv, we will be able to "recapture" lost money on a slider, or just tell a world not to bother on a particular Slider when others are allowed to. Have to wait and see what is in GC2 (and hopefully, GC3!)