[randomtoast]

> most places just don't have enough people walking far to make them worth it

I would place them in the city centers of major cities, as there should be more than enough potential users.

> They also block people who are trying to cross the street.

Cities could be redesigned by banning cars from their centers, as is already the case in several places around the world.

[bluGill]

Moving sidewalks are worse than cars. At least with cars if you want to cross in the middle of the block you might find a break in traffic where you can do it. The moving sidewalk blocks crossing the street (except at intersections) 100% of the time.