So, looking at all of the above, I get:
1. Give the measuring cups back to the Missus and weigh your priming sugar. Exception could be if you are very careful and using table sugar, which is very consistent.
2. The old 3/4 cup thing was for writer convenience and gives over carbonation for most styles.
3. Use a priming calculator with the temp set at around 70 F. Most beers we brew finish fermenting in the 66-75 F range, even lagers with a D rest.
4. Some of the priming calculators do go to too fine a point. Do you really need to weigh your priming sugar to a hundredth of an oz.
5. RHAHB You probably can't tell the difference between 2.4 volumes of CO2 in a beer and 2.5 volumes. At 2.7 or more, yeah.