good to hear you find out great workarounds really missing from the engine features.

if there is an interest I could add to my editor auto multitexturing based on height and slope data, which are available at the moment so it would be fast. next edition is almost ready I just have to add a new simple free camera mode, and to remove some unused/unnecessary data related to RTS AI.

...what I have ever wanted to check is the scripts of the extra terrain toolset of unity 3, I don't know it is still okay with unity 4. it contained some random terrain heightmap generation and nice simulation of different kind of erosions afterwards.