Detroit has a bright future ahead of it. All the evidence suggests that it hit bottom a while ago and is rebounding. People really should visit and see first hand (in the summer, if the weather is that important to you).
I couldn't disagree more - if the weather is important to you, visit any time but the summer. Preferably the fall or spring, but winter is okay if you're prepared for it (it just goes on way too long).
(I have little experience of Detroit proper, but I assume the weather is sufficiently similar to Lansing and A2)