I've seen a lot of variability. High season for tourism tends to be in summer given the more temperate climate versus points south, but there is some serious wealth in BDA, and a fair bit of business travel for the financial services industry. That said, I've not missed an upgrade in the past few years, but I don't recall F going with empty seats, though there have been some light loads in Y. That's what usually takes me there and I append vacation time if I can.

redtop43 appears to fly the route a lot and probably has a better overall handle on recent F loads though.

Most of the folks I know from the US who go there actually tend to go via cruise ship rather than flying unless they plan to spend a week or more there or have property in BDA.

Back in 2003, I was the only passenger on a PHL-BDA 757 in the days immediately following Hurricane Fabian, but apparently we had a full load of relief supply cargo. I wound up having to rent a house for a week since more than half the hotel rooms were unavailable due to storm damage. It was interesting and rather fulfilling to both do consulting by day and lend a hand in storm cleanup in the evening.