Burn it down. All of it. Seriously; in its current physical state it can't be saved and its very existence makes a mockery of America.
Detroit isn't what does that. America is worse than just Detroit. America is a horror from sea to shining sea, with every rat caught in the middle carrying the horror in his desperate, trapped little heart. Burning Detroit down wouldn't chance a single thing about the horror.
What would help Detroit, and America, would be the guillotine, applied liberally upon the upper classes. Burn down Palm Beach, not Detroit.