I think a big problem is the fact that SDC is set on the top of a mountain, so finding land that can be used for building is kinda hard to come by. I mean, SDC currently occupies 61 acres on very hilly ground. In comparison, the public areas of Disneyland cover 85 acres of flat land in the middle of Anaheim, with little room to grow after having converted a large part of their parking to build California Adventure; Magic Kingdom is 107 acres of flat land; Hollywood Studios is 135 acres; Epcot is practically two parks in one with 300 acres; and Animal Kingdom, with all its land for the animals, clocks in at over 500 acres.
So it was probably inevitable that the land where Wilson's Farm is was going to be used for further expansion.
I know there are areas where construction can't occur because of the cave, right? Where are these areas? Do we know how much land exactly is available for expanding the park?
This is why I wish they'd realized that to make Celebration City work, they needed to keep it open later. 10pm for a "nighttime" park was just not feasible. If CC had lasted, a lot of their expansion ride-wise could have been done there, leaving more open for SDC.