Here's one big difference between Mt. Clemens and the Oakland County communities mentioned earlier in the thread: Most of those Oakland County communities, save Birmingham, you drive through downtown on the main roads: Ferndale you have Woodward and 9 Mile, both of which go through downtown; Royal Oak is bypassed by Woodward but Main and 11 Mile both go through downtown; Birmingham is slightly bypassed by Woodward but 15 Mile goes through downtown.

M-3 goes around downtown Mt. Clemens, not through it, and there is no major traffic generating east-west road. M-59 is a couple miles north of Mt. Clemens and in fact never enters the city at all. So most of the people driving near Mt. Clemens never even see the downtown.

M-59 has taken the retail thunder away from every community in south and central Macomb County. It is an absolute economic disaster, and it is also partly to blame for Mt. Clemens' difficulties. But I think mostly the "hidden" downtown is to blame.