I grew up in Michigan, and I can say with a good amount of certainty: any house in Detroit that is unoccupied does not have a single thing of value left in it, especially copper. Even some places that are occupied have had their copper stripped from them, sometimes live wires that results in the death of the thief.

EDIT: Some links. Copper theft is a big deal in Detroit.

City of Detroit borrowing a page from scrappers and thieves by selling old copper wire to boost Detroit's finances.

http://www.detroitnews.com/story/news/local/wayne-county/201...

Thieves stole copper from functioning pumping stations, leading to massive flooding in Detroit recently

http://detroit.cbslocal.com/2014/08/13/copper-theft-a-possib...

Copper thieves caught in a sting on camera

http://www.wxyz.com/news/local-news/investigations/copper-th...