For those of you who have never been to the Woodward Ave. Cruise, just GOOGLE it. There are 73 pages devoted to it.
Trust me, it's not just for people who love classic cars. You will see anything and everything "car" related cruising the Blvd. Old cars, current, and the Big 3 even roll out their "Idea" cars, and if they aren't displaying them, they're usually driving them.
I've seen cars with license plates from practically every state in the Union, and every year it just seems to get bigger and better.
The "locals" set up lawn chairs the whole entire route, and it truly becomes an automotive circus. (There's even a car show at the entrance of a cemetery). Even the local Police departments are pretty cool about it. (as long as things don't get too far out of hand).
Things actually get started several days before the big Saturday event. But Saturday is the official cruise day that you don't want to miss.
As Fuzz40 pointed out, seeing the Chrysler museum would be an excellent idea, maybe on Friday, and the Henry Ford museum is another place everybody should see at least once in their life. (Just allow yourself at least 4 or 5 hours to take it all in).
If you live within a 12 hour drive of Detroit, I honestly think you wouldn't be sorry that you made the trip. Besides, 12 hours in a Crossfire is just getting settled in.