I have been thinking about this to lately. And the only one I think is of concern (and could quite possibly I could be entirely wrong) is your fourth point. A horse that like to lead is going to be disadvantaged from a outside barrier because they have to make sure they get across and dont get caught wide. On the other hand, I dont believe a barrier draw really matter to a horse that sits at the back of the pack, and swoops on the leaders in the last turn and onto the straight. I guess though to be able to decide that, you need to have reasonably accurate speed maps, to determine the horses running position.

I guess by the same token, if you are using speed maps, and there is only one horse that likes to lead, and looks as though no one will contest it, then I guess a wide barrier is not so much of a concern.