^You're welcome, Coaster.
I think SDC attendance would really suffer if a Disney park opened in southern Missouri, mainly because of the name recognition, like you said. The long term effect would all depend on the size and theming of the Disney park. I'm sure the Disney park would be much larger, more focused on larger thrill rides, and (most importantly) less personable than SDC. So, assuming that SDC could weather the early storm of novelty for the Disney park, I think SDC could coexist with a Disney park in the vicinity.
That being said, I'm with you. I don't believe Disney would ever build a park in southern Missouri. I don't think it's a very viable area for them.