Yes, but then you're committing commuters from the Rockaways to both a long ride across Queens, and then local service along QB until at least Roosevelt, at which point the exp trains are quite crowded. I agree it's the most realistic solution, but I don't think it's a great one.
I do agree with the fumigation thing though.
As for development, Sunnyside is attractive because of its building stock, and even then, that's irrelevant as they are building things there. SI has very run of the mill, low density building stock (nothing crazily special) and therefore would be extremely susceptible to development.
Also, I don't really see your point. All you're proving is that subways raise real estate prices, which is....exactly what I'm saying will happen.