How long do you stay somewhere to justify the really expensive flights?

Couldn’t find another post that asked this specific question. But let me know if there is one :)

I’m planning to fly from New Zealand to NYC for a solo trip this October. Flying domestically in USA doesn’t get too pricey and I see lots of Americans talking about visiting NYC for a weekend or a week but coming from NZ I’m looking at spending about $2,500 NZD on a return trip . This wouldn’t break the bank for me but it’s still a lot of money. I feel like I would only need a week to get the most out of New York City without getting bored or travel fatigued but I also feel like I need to stay longer to justify what I’m spending on flights. Imagine flying from New York to New Zealand and only staying for a week. Surely if you’re traveling all that way you stay a little longer. Worth noting in my personal situation I could afford to go for about 2 or 3 weeks, just not sure if I should save that time off work/money for another trip in the future.

I’m a little torn on this one. What do my fellow solo travelers here think? Is it worth flying halfway across the world for a week long trip?

Thanks :)

How long do you stay somewhere to justify the really expensive flights?