I am curious: does anyone use the Poser face room textures? If so, what are they good for? I am still learning Poser, but they always look revolting on my figures, whether or not I match the face colour to the figure. Even if I tell it to match, it never really matches.

I thought the Face Room textures might be useful for toon renders, but no. If I put on a face room texture, I can't get Poser to do a proper toon render with it - it looks just the same as in the preview, even though I set up the face material for a toon render.

It seems to me a far better idea to use a quality texture and just modify the shape in the face room. Am I missing something important, or is the whole business of modifying face textures in the face room quite pointless?

The Face Room, at best, is a good start to create a new character using a model base from a photo.  Unfortunately, Poser does not do a very good job of it that other, high-end programs can accomplish.  Plus you are only restricted to specific models, not the millennium figures or some others commonly used.  I am afraid you will need to create your textures the conventional way others use, a 2D program like Photoshop or Paint Shop Pro.  It is far easier to take this approach than deal with the Face Room learning curve.
Many Poser users prefer to either morph their characters using morph packs or other 3D programs allowing direct manipulation of the polygon mesh.  Again, there is a learning curve involved but can be mastered very quickly.  Morph Targets created by other programs can be loaded into Poser resulting in a new dial setting placed into the model's properties.  With morph packs installed, you can alter your model within Poser and save your new creation right in the library. 

I am getting good results modifying the face shape of G2 characters in the Face Room, provided I stick with the original textures, or textures from characters that I have bought. It baffles me that the texture modification function even exists in the Face Room, because it seems a total waste of energy.

I tried creating new characters from photos, but that is beyond my skill level at the moment, and even if I get an acceptable result, there is still the problem of matching the body texture to the face. So for now, I seem to be limited to the G2 figures and the available characters for them

If you have morph packs for any other models, you can adjust and tweak settings in the Pose Room without setting foot into the Face Room.  I have done numerous customs for my own use that way.  That way, I can use any other texture maps from other vendors for a complete face and body match.  Besides, the Millennium figures are not supported in the Face Room anyway.  Now there are individuals that use 3rd party 3D programs to completely customize character morphs.  I have used Argile on occassions but I am not that proficient at custom morphing just yet.

The book, Practical  Poser6, Chapter6, Creating Custom Faces, Page 127, Texture Variation.
This explains head and body matching for Face Room compatible figures.