OP,
For me, the Prestige card has been fantastic, even with the recent benefit reductions I will be keeping the card. However, I'm located internationally in Asia, and the lounges here are generally better than the ones back home. That said, I also often travel with my kids, and lounge access has been a HUGE benefit. My wife is obssessed with worrying about the kids eating enough, so she feeds them at every airport we ever go to. Even snacks are fine, as long as they eat so the lounge offerings have always done the trick. With 4 of us, it's a considerable savings for some soft drinks or juices and snacks when we travel.
Value is very personal however, depending on your circumstances. For you, I wouldn't even bother considering the Amex.
Is there a PP lounge in the airports you usually travel through? Obviously, this is the big one. Without the right lounges at the airports, any membership is worthless. Also important, are those lounge offerings adequate?
Do you guys ever fly separately, or with extra friends/relatives? Each AU gets their own PP with the full self plus 2 guest benefit. Thats 6 people total if your spouse is also an AU.
Do you or your guests drink? If you drink alchohol, you will definitely get your money's worth with a free beer now and then (I don't drink).
Do you generally grab a bite to eat, if so are you relatively picky? The lounges near me are really pretty good. Plenty of hot and cold options. However, last time I was back home it was still decent with some sandwiches, veggies, and soup.
Ultimately, I would focus on these things. 100% worth it for me, even if I have to go back to domestic lounges one day I will keep the card. Don't forget the fourth night free benefit for hotels with this card as well, and from what I understand you can still use the airline credit to purchase airline gift cards. Maybe a Christmas gift idea!