Short answer to my own question after collecting a small sample size: the number of seats in the V bucket more than a week before a flight mean very little when trying to predict the chances of an upgrade.

The details:
When shopping in advance, I used to look for V7 flights and choose them over flights with less V availability.

But then I noticed that flights showing something like F9 A4 V4 a week out usually ended up full by the PM window with a long GIDS list and no upgrade. Just this week, though, I snagged a gate upgrade on a flight that showed V0 months out, and F0 A0 V0 for a full week before the flight.

So at least for a GM flying between Florida and Socal, the number of V and A/F seats available more than a few days before a flight appears to have little or no correlation between actual upgrades.