I saw one that fit your description here but it's for Half-Life 2: http://www.planethalflife.com/half-life2/videos/
Look under the heading with SIGGRAPH videos.
I think the purpose was to reduce engine overhead by reducing polys using some pretty trick shaders or bumpmaps or something to do with the lightmap but the original model used to create the 3D texture is high poly so the complex work still needs to be done - usually with some high end modelling software.
On the thread topic, game value is obviously enhanced if user created content matches or exceeds the original game quality. Doom, Quake, Duke3D, Quake 2 and Half-Life were excellent value. It's too bad that high cost, newer games aren't seeing nearly as many user mods and that could be due to more work required as well as more powerful tools and knowledge. Also, more games on the market divides the user community since we're well past the days when Quake was the only game in town.
If you look at the number of quality SP mods for RtCW, Unreal 2, Deus-Ex, Undying and draw the trend line into Invisible War, Painkiller, Doom 3 etc. it's looking as if you can't factor user mods into the enjoyment/cost equation in deciding whether or not to buy. What's in the box is likely your only trade for the money.