Whenever dealers at a convention feel like their under served, it's a valid concern. Especially if they work in the field related to con itself. The are a variety of solutions (I don't claim to how these ideas survive the crash test against a reality check, though), like cheaper artist tables, going to smaller convention, creating co-splay partnerships.
On the other hand, I've seen cosplay be a major component to increased attendance at smaller cons and pushing the geek culture mainstream.
And as for the one con that I've seen that made cosplayers feel unwelcome, it seemed to be my worst fears of what what would happen to geektown. i.e. a much smaller convention with a much older crowd asking itself if all of the "serious" cons are dying out and asking "where did all the new blood go?"
How old? I once counted about five motorized scooters making their way across the street from the hotel to the convention hall.