I have sympathy for the OP in both situations, as I feel the Hertz reps can and should have done better. But neither situation is so cut-and-dried that the OP didn't share some responsibility, either.

1) Why didn't the OP rent at the airport to begin with? I suspect it was because the rental was several hundred dollars more expensive. Well, now they know why. And abandoning the whole trip at that point was a choice--they could have chosen to pay the extra $700 to salvage the rest of the trip but instead chose to cut things short and just go home.
2) I don't see how this one "ruined the vacation", as the OP even stated they didn't think the plastic cover flying off was that big a deal and they just enjoyed the rest of their trip. It's certainly a downer at the end to be told one must pay $1,600 for something out of their control, but there's time to fight that, investigate credit card insurance, etc. after getting home.