First of all, try working in an orderly way! Organize your nodes into groups, at least have them lining up nicely, instead of making such a mess. Especially when having a few hundred nodes, it is paramount to have some structure. And give your nodes unique and describing names, so you can later easily recognize what certain nodes do. I often write (very) brief sentences in the node name, or even why it cannot have smoothing on, or what range of values are good, e.g.
Maybe the thing with the hero rock is the smoothing of surrounding area (masked out by a simple shape or so. I don't know the file, but that seems logical. So, then if you place the rock in line, and it smooths out all except the rock area, the mountain will disappear. Try adding a compute terrain after the mountain and before the hero rock, or at least a 'tex coords from XYZ' shader (which kind of freezes displacement before it).
On the aerial view thing; you can try if it works on your machine. Doesn't need to be very taxing at all. The main thing is making a good number of masks in Photoshop (greyscale 8-bit of good enough resolution), and masking a line of surface shaders with them, each with their own set of (procedural) textures. And also masks for objects like trees, and shrub, etc.
