I´m running into various issues with Lightmaps. It all comes to down to the fact that you cannot access lightmaps or lightmap settings by object. More info of what my issues are can be found here.
I mean the lightmaps are related to a certain object, obviously so it should be possible tell wich lightmap is used for wich object. And settings like mipmaps or compression probabely shouldn´t be a problem for the renderer if they differ from one object to another. Can´t these settings and the related lightmap be exposed per object ? So you could disable compression for a certain object before rendering. Or change mipmap settings afterwards, when artefacts occur. In theory it´s possible to do this in the current state of the interface, it´s just impossible to find a related lightmap once a level reaches a certain size. Lighting Quality, speed, and flexibility could be improved if per object settings would be available.