As discussed in your linked thread, it is a CEZ, and as such concealed carry cannot be recommended unless you are okay with violating the law, and this is something I would advise particular caution about to any activist who is probably already under the watchful eye of big brother. Even if you don't consider the arena part of the hall, remember that the seating capacity of cobo hall's classrooms far exceeds 2500.
I would almost never ever tell a good person not to carry, and this case is no exception. Just remember the overall quality of their court system, as demonstrated by theszerdi's case. They seem like they care less in court about determining the validity of SD shootings than prosecuting someone following all laws. So going there actually violating the law in a manner that would annoy them, it is something that requires extreme caution and consideration.
Regardless of what you do, I don't think you'll encounter metal detectors there. I carried a big folding fighting knife to the SAE congress in 2009, in the pocket of my suit.
I think there were signs that said "all persons subject to visual search" or some nonsense like that. I think they said bags were also subject to physical search, though no one I remember was carrying any. It was such a formal event that it didn't seem like they wanted to search anyone, though the auto show is certainly far less formal, and as such I wouldn't be surprised if they do some pat downs or something.
OC is the only for sure legal carry there, and it seems like it should be the next AB&E issue. Though I must say, just like with AB&E, there is no way in hell I'd want to OC there.