Well put, but with this - "Other than perhaps a little extra calcium, it doesn't take extra food mass or high nutrition during pregnancy to make for a healthy litter"
The contibution to the health of the mother through being well fed/etc is not being accounted for which may garner benefits.

Some more tidbits from the paper I found on the females contribution via the placental membrane - placental provision of water and sodium both exceed what is in the yolk supply.

"But then there's the argument about mass. While source material can be converted to denser material, it stands to reason that the amount of mass, or total weight of the converted material should not exceed that of the source unless additional material is being added during the conversion process."

Again the 'law' of conversion accounts for energy not being lost or, indeed, expended, and therefore adding mass to something even when this added particle does not have any weight but simply changes the structure, this is a possibillity in an open system, etc, etc (physics bores me). Certainly food intake + heat here would equal both a source of energy/additional source material. At the same time when we debated the possible role of water in the initial weight gain this seems now a very likely contributing factor considering the proven placental contributions.

At any rate there's definite evidence that a combination of both captital and income breeding both feature in the cycle as a whole.
I definitely agree that nutritional intake around the year is very important but still think it's just as important during pregnancy regardless of capital investment in the early stages.