Last summer I replaced an iPhone 6 or 6s with a 7 that cost about $500, or half the cost of the new, high-end phones. I don't perceive the new ones to offer 2x the value of a new or refurbished 7.
I actually prefer the iPhone 7 to the X and even S9, I see very little reason to get anything newer.
Only 2 drawbacks: not AMOLED (would add $100-$150, did not consider it worth), mediocre camera, which I rarely use anyway.