"I've recently been frustrated by Poser's tendency to smooth out a face mesh too much in some places where there should be sharper edges, specifically around nostrils and ears.  Does the subD smoothing help at all in areas like this?"

Nope. If there isn't enough mesh around the critical areas, the new subdivision will smooth it just as the old native Poser polygon smoothing does.

While the type of Pixar SubD SmithMicro used can respect hard/creased edges, there currently seems to be no way to add those type of edges to a standard wavefront object.

I just made an experiment using Stehanie-I-LoRes' head.

I added some hard edges around the ears and the nose which showed up in Poser and Wings3D, but SubD level 1 and 2 ignored them and completely smoothed them out.