Well, there are some technologies that allow a lot of detail without using GBs of textures ( procedural generation of erosion data, vegetation data, roads, cities, and so on ). So "larger areas = less details" is not entirely true.
With such technology, you can concentrate details in some ares ( like a "persian gulf" area ) and let other areas be procedurally generated while you fly over them just to fill the gap.
In the long run, to me this option wouldn't be so bad.