I'm upgrading to the X, but I ordered a 8 Plus for my wife and will be using it on my line until the X arrives (she doesn't care when she gets a new phone). LOL
Anyway, here are the things I regard as important for this year's upgrades:
1) CAMERA. Camera is always at the top of my life. Specifically, the capability of shooting 4k/60fps is a big deal to me. I shot almost exclusively in 4k on my 7 Plus, but I always wished the video had a smoother frame rate. It also gives you some latitude for slow-mo (including the 240fps slow-motion mode in 1080p). In addition, it may be 12 megapixels still, but they specifically mentioned a new sensor in this year's phone. It will be interesting to see which sensor they are using this year (my guess is it's the same as the one Samsung is using, which has slightly larger pixels than the one in the 7 Plus from last year). The improved ISP should help too, so I expected a modest but noticeable improvement in low-light photography on the 8. Of course, the X is going to be even better with its faster tele lens (F2.4 vs F2.8) and OIS on the tele lens as well. And finally, I'm really interesting in seeing how the new Portrait Lighting mode works and the scene detection. Overall, I think the camera improvements seem to be pretty good, but we'll have to see for sure when the phone comes out.
2) BIONIC CPU & APPLE GPU. This new SOC is killing it in benchmarks, but will it result in even better fluidity and response time? Will apps open even faster? Will encoding and decoding be much faster? Hard to say how much real world difference we'll notice, but one can't help but marvel at Apple's chip design. Either way, this new combo should be able to handle gaming and AR with ease.
3) WIRELESS CHARGING. I think Apple's new wireless charging pad looks cool when it comes out next year, but I'm personally not that wowed by wireless charging. I've been using it on my Samsung phones for the last couple of years, but it's not a game-changer to me. Maybe when they actually have proximity wireless changing in phones it'll make a big difference, but as it stands, it's just not that compelling to place a phone on a wired pad to charge the phone. It's nice when you are at a desk and just want to lay the phone down for a bit to top it off, but most of the time I'm either 1) using my phone while it's charging plugged in, or 2) charging it overnight when wireless charging makes no difference anyway.
4) SPEAKER. 25% increase in speaker volume sounds good, but how noticeable will it be? The iPhone 7 already had pretty decent speakers, but I'll take improvements, especially if the quality remains good with the increase in volume.
5) TRUE TONE SCREEN. I personally don't care about this, but I supposed it's nice to have. The Promotion 120 refresh rate would have made more difference.
6) GOLD COLOR. Not a new "feature" as rightly pointed out, but I think the new color looks great and that's what I ordered for my wife because she liked the way it looked.
SUMMARY: If there was no X, I would only be upgrading to the 8 Plus because of the yearly upgrade path we are on. But it's a more compelling upgrade for someone still on the 6s Plus (many people are still on a 2-year upgrade path, so for these folks, it's a great upgrade). I'm really excited about the X though, but I'm not expecting to be able to get it until very late in the year (or maybe even early next year).