Thank you giorginho , Carpacchio and Knobbgb .

I'm thinking we will see what happens at the airport. We are spending 2 days in Athens before we fly to Santorini so I'm not sure we would have much time for the lounge and/or it probably wouldn't be worth it.

I will check out the bidding upgrade since there's no commitment but it's sounding like we should take our chances. Our carryon bags will not be oversized but may/will probably be overweight.

We are already bringing under-the-seat backpacks which will probably also be full (15 day trip with no checked bags means we have to maximize) so probably no option to offload extra weight into the personal item.

It does make me nervous that you are all recommending documenting the contents of our bags specifically for this flight (or was that a general recommendation?). I would do that anyway but it sounds like there's a larger-than-usual chance they would get lost? Since our flights originate in Athens (we are not coming from another connection), it seems like the probability of loss should be minimal?