Having spies in every city (border cities by 1 AD--others later) has been part of my strategy. During recent games I have been running more counter espionage. Simutaneously, I might have been raising my slider higher than I needed. "Spread culture" probably has a negligible effect to slow down a neighbor's cultural victory anyway. Still, it is nice to see where a neighbor is producing spaceship parts to sabatoge them. I'll try those strategies alone with the slider at 10% instead of 50% and see if it is just as effective. I can't really afford to raise the slider until the spaceship techs are researched anyways.
Ultimately, I would like to learn how to get my beakers high sooner so I can get my spaceships launched before my adversaries get all the nice espionage techs at the end.