Hey Luis, I remember this being discussed in the past,....Me,..I could never see doing a house wash without cleaning the gutters. So when I give a quote on a house wash the gutters are part of that. Calling it an add on service seems to be too much like "nickel and diming" the customer. I think most just assume that is part of siding wash.
Not sure what you're using as a house wash mix that removes gutter streaks but it must be good stuff. My mix we make regular dirty gutters look better,..but using a good gutter cleaner will make them BEST,..whether they're striped or not.
Jeff