Some interesting points, thanks very much. Though I'm not sure I get the point about checkin queues (lines). Same wherever we drop off the car, no?

There is also the good point of needing the car that evening. I think almost certainly that we would want to drive out from the hotel for our "last meal" in which case we would already have incurred the hotel parking fee.

I think on balance we may stick to original plan of returning to the main Hertz depot which, I understand, is less than a mile away. So we could also take our time that evening to fill up with fuel at our leisure.