History Buff, while an interesting idea, I don't think that is the answer for GE. When we think of SDC, we think of a "glorified 1880s" - something that never really existed but we wish it had. (This is sort of like the Golden Era of Hollywood themed parks)
I personally feel that Grand Expo is fine as is for the time being. Can it be improved upon? Sure. However I do not feel that its theme is so pressing that it ruins the entire park. When an appropriate retheme presents itself, it will compliment a new addition to the area.