make your planet as segments, across and down, attach them as limbs to each other and hide and show the visible ones, so anything in screen is shown and off screen is hidden, build your bumpy scenery into the model segments, I don`t think a bumpmapped texture would work since DB collision works on the models data dimensions, not what the texture is doing, so you would fly through bumpmapped cliffs (I think you would anyway), segments could be relativley low poly and allow you add luxuries like caves to fly into, overhanging cliff edges, sky islands etc.
Tyger software