Hmm, that is an interesting thought regarding importing meshes directly, but it could get rather complicated, and allowing any mesh to be imported would present the issue of not knowing whether the mesh being imported is voxel-based or not. I am not going to completely rule out the possibility of allowing larger voxel grid, but it will be later on once I am able to revisit that. Apologies for not being able to help with that for now, and hopefully it is something you can work around.
Also, that is a good suggestion about only saving the frames that have changed. I recently enhanced the editor to not generate the meshes again if only a property was changed, so I could probably expand upon that and keep track of which frames where changed/added.
I am glad you found RPG in a Box and I hope you are having fun with it! :)