More anecdote FWIW:
1. I said no to a $3500 one-week spring break school-advocated "Spanish" trip to Central America in 10th grade. It struck me as minimal value for the money and an excuse to hang out on the beach and do poverty tourism and call it "educational."
2. After much debate and angst, I said yes to a $4500 3-week band tour through France and Germany, where the kids played concerts in local churches and town halls almost every night, the summer after 9th grade. My gut reaction was that it was way too much money. But we could afford it, and on a per-week basis the cost was reasonable, and I thought DD would bloom given that degree of independence (the line from "Pride and Prejudice" springs to mind that she wouldn't rest until she had exposed herself somewhere), and it so happened that the end of the tour coincided with when we planned to be in Europe anyway for a family vacation and so we were going to have to buy her a plane ticket anyway, and between that and the avoided costs of summer camp etc., the delta was probably closer to $2-3K. So I said yes and told her that we would pay the fees and she was responsible for all spending money (the kids were on their own for lunches, so it was like $700). And amazingly, my total spendthrift kid saved almost all of her allowance and student aide money, and she and a friend threw a big bake sale that made $300 between them, and 9 months later when it was time to go, she had like $850 saved.
I wouldn't call any of this mustachian -- it was a totally frivolous luxury that she's damn lucky we can afford to give her. But it was worth it for her and for us.