One of the disadvantages to using subdivided displacements is that unless you later convert them to models with a decent model unwrap, you're going to get horrible texture misalignments at your seems.. I'd be concerned about this, but i'm sure you're experienced enough to have taken this into account already? But i figured i'd give a heads up anyway.. You're a wizz with the entities but i'm unaware of your experience with the rest of Hammer's feature's and practical tendancies.
edit: ok, i seem to have failed at reading the last page. But i'll leave my comment as it still kinda stands i guess. Making some custom textures to the same vertical scales as the displacements might help. Depending on what materials you have intended for them.