According to Sheldon (pbuh), spreading is not needed when going up one step. He says something like the angle of the dropouts won't be too great to cause harm. One of my bikes, I haven't spread the stays yet and it is fine, but I will spread them. Even though no problems will most likely happen, I figure I'd get it spread so that the dropouts line up correctly. Why put extra strain on the axel when you don't need to?