You make some really good points. Things I had not thought about, like the idea of an optimum fineness. My curiosity got the best of me. So I built some parts in ROCSIM. I realize that it is not a wind tunnel. But it was interesting to see the results.
Optimize for Cd
First came the nosecone alone. Just like you said there is a dip in Cd. The Cd falls quickly from 1:1 down to about 2.5:1. The minimum looks like it is between 3:1 and 3.125:1. Then it rises smoothly and gently all the way out to 8:1 where I stopped. So there is an optimum fineness for Cd.
Next came a BT60 3FNC rocket with an ogive nosecone. I checked out the Cd as I changed the fineness ratio from 1 to 6 in 0.5 increments and also Mach numbers at 0, .24, .5, .75, and .99. I found no dip.
Finally I tried a BT60 tube alone. Again there was no dip.
I think this means savings in the Cd from an optimal ogive nosecone are swamped by the effect of the rest of airframe.
Optimize for weight
I looked at the increase in weight. Basically it appears to increases linearly. As the fineness increases the Cg does shift forward. So, I am not sure there is an optimum fineness for weight.
Optimize for volume.
I remembered that the best packing shape in terms of minimum surface area and maximum volume is the sphere. If you took a sphere and squished it, without changing the volume, the surface area would have to expand. This means the shape that comes from deforming a sphere are not as efficient as the sphere. Then I thought about a nosecone like a hemisphere that got stretched. As long as you leave it rounded, it should work the same way a sphere does. This suggests there is no optimal fineness ratio.
I am not sure I have thought about this right. What do you think?