Unfortunately no solution has been found yet. We have the same problem. What we realized lately is that if one only adds images which are in close vicinity to each other everything works fine. No blurring. But if one adds couple of images which are distant to the current view (e.g. USA <-> Europe), the blurring occurs when the camera is tilted too far.
With that in mind my suggestion would be to add a culling to the images dependent on the distance to the camera. But I didn't have the chance to test it yet.
The draping of an image uses projective texturing, and it has stretch the image over the entire projected area. It can only approximate the extent of the terrain in view, and so you get this blurring artifact. A long-term solution might be to use cascading (as with shadow maps) but that's not on the roadmap at the moment (i.e., not funded).