In general, the whole scenery has mip-maps, except for very specific cases, like small detail texture that are not visible from far away.
As an exception, directional shadows textures, which are separate from the base building textures were, were made without mip-maps, because this saved some texture size (there 5 of them at 4096x4096, and they grow from 16 to 22 MB each, with mip-maps), so we assumed it might saved a bit of ram too, because those texture, being basically black/white and without any inherent detail, don't create much problem without mip-maps. But yes, this can be dependent on the drivers configuration too.
The good news is that, alongside all the different tests we keep making about memory allocation, we found that adding mip-maps doesn't increase the RAM requirement in a measurable way, and it saves a bit of GPU memory too. I don't see much different in the visual appearance either, but perhaps if you see lots of shimmering, they might help you, so I believe we can safely add them without many issues.