Would it be a great idea to save advertising space, or place for art, on freshly poured cement sidewalks?

No, we’re already bombarded by advertising at every turn as it is.

No. There is enough eye pollution now without wasting perfectly good concrete, as well as the materials and natural gas ( heating products) to create the concrete.

One of the tricks of good advertising is to get the message out to the greatest amount of people for the least price in a way that everyone will notice. That’s one reason I would shun the concrete ad idea.