Here is a quick demonstration I created a couple months ago for a user group event that shows how you can use a couple of the graphite modeling tools to rebuild an landscape model that has a ton of problems.

Anyone in the design viz industry who has ever dealt with imported landscape geometry can probably back me up that more often then not these things are a big pain in the butt. I've seen this same problem in games when trying to use real landscape data to derive games landscapes. Versions of this workflow could obviously also be used for scanned models. Don't forget to set the video to HD for higher quality.