Take it from a person that just recently wasted a lot of money on an 8+. My wife had a 6+ for about 3 years and in late 2017 she started have weird battery issues. It would drop from like 90 to 30% to zero in a matter of minutes. We reset the whole phone that didn't work, we took it into the Apple store and they said the battery was fine, etc. This was before the whole battery thing from Apple. Finally I said screw it and got her an 8+. Her new phone is nice and everything but there is very little difference between her old 6+ and the 8+ besides the battery. If I had the chance again, I would have them replace the battery. This was my fault for not getting a battery and my wife's fault for being an Apple fanboy. I guess the bright side is that I didn't spring an extra $300 for the X.
I think the problem is that it use to be that every two years when you upgraded you'd spend $500 but get a lot better phone. No you spend $1,000 and barely notice a difference in speed, no additional space, same or worse battery life, lose a headphone jack, very little difference in screens, etc. I think the best thing to do know is wait 3 years between upgrading and when you do get a $400 phone that has the same specs as a 6 month old $1,000 phone.
I did fail to mention that her 8+ does have wireless charging, which she really likes. I told her about 5 years ago that I really liked it on my 2013 Nexus 5....