The area you have covered in blue, includes first aid and a rest room, I don't see either of those being relocated.
I merely pointed out that there is plenty of room in that spot, as they can always build behind the restrooms and the first aid location is kinda hidden so they can move that up in line with the restrooms or move it to another unused building in the park like across from the Log Flume/American Thunder. The only thing I ain't sure of is all of the other smaller buildings they hide behind the blue wall, I have no idea if those are important to that area or not.
That area in blue would require the restroom be relocated, the huge mechanical building behind the restroom be relocated, the A/C chiller unit that supplies cooling water to the west half of the park be relocated, the "ice house" building that produces all the ice for the entire park, would possible block the only access to Mr. Freeze island for vehicles and cranes, an emergency generator, and of course first aid which can not be relocated anywhere other than on the edge of the park as it currently is. This is due to it needs to be able to be accessible to city ambulances without them entering the park itself. Plus the whole area beside first aid is pretty much a swampy wet creek.
I think if the park decides to build over an existing area, the first aid spot will be pretty low on that list. I could see them using the tidal wave area, the old petting zoo area in front of colossus, or Old Glory first.
Yep. Changing that area would require a large investment, beyond just the ride/construction cost.
Removing Old Glory would provide a large amount of space. Hopefully it gets utilized at some point.