DP makes some good points. Perhaps there's a reason why these places aren't highlighted. Such as them not having the money to advertise or the willingness to spend to be part of Visit Detroit. In the case of The Henry Ford, I'm sure they are comfortable with their exposure and marketing efforts considering they are one of the top tourist attractions in the entire state.

I have no expertise in the local travel industry, so I don't know. If it's a matter of finances, perhaps organizing a collaboration that can then advertise together [[i.e. Wayne County Historic Downtowns). I really don't know. But to me, the first step seems to be to find out why these places aren't part of Visit Detroit...then formulating a plan to get them recognized and/or organized.