Both of these I have around here and there and have to admit, it would be really nice to have them in the engine.
simplify a mesh by decimation
This one is tricky. I have never delved into animation so I’m pretty useless right now on that front, but the decimator I have with a couple of days work or more would work fine with static meshes (positions, normals, texCoords, colors maybe…).
There is a mesh boolean operation tool around you might like to take a peek at (using shapes as masks).
Not tried it yet, but I am considering to use yours instead of JME LOD generator. My understanding is JME’s default LOD generator only modifies the position or index buffer and it has no problem with animation, so my understanding is your decimator should have no problem either. I might be wrong so.