It depends on the scale of your terrain; the larger the represented landmass the less information is represented in your export. Any small details will not transfer to even a reasonably sized heightmap. I've been playing with different workflows lately but haven't found any silver bullet. Often times my approach is radically different depending on what type of terrain I'm working with.
Sometimes I export a high resolution heightmap, slap it in blender, separate the mesh into subdivisions and use that mesh for my terrain instead, and use the voxel technology when it makes sense (caves, overhangs, etc). To texture, I export a full selection of maps from WM like mud, water flow, different height scales, etc and use those to compose my base texture. Very ad-hoc and has a ton of disadvantages (manual LOD creation and texture fidelity near the camera come to mind).
At this point, it really requires a lot of experimentation.
Hope that helps!
Nvidia 660 - Driver 340.43
8 Gigs RAM