OK, I got the porcelain thing figured out. The problem was that it's effect is only visible in renderings, not in shaded mode. This may seem painfully obvious to some, but I found absolutely no mention at all of this simple fact in any available docs, Martin's Tech Notes, or in any post revealed by a forum search. So here for posterity is what I learned about applying Porcelain:
1. Porcelain effect is not visible in shaded views, only rendered views.
2. Black, blotchy surfaces in models using porcelain are caused by patches with normals turned wrong way around.
3. Strange spline artifacts can be eliminated by a) saving, closing and reopening the model after porcelain has been applied and rendering twice in a row - sometimes the renderer doesn't get the normal blending right the first time.
Now that I got it working it's really cool. My model looks sooo smooth. I thought at first that the porcelain/normal thing would be a pain but it actually turns out to be a great way to quickly find the areas where normals are reversed. Porcelain clearly shows the trouble spots, then the 'normal hairs' show the exact patches that need flipping.
OK, enough blather. I'll post an updated model in the next day or two for comments, etc.
B-