The jump from the 6s to 7 was significant and I don't see why many people in this thread feel that isn't the case. Water/dust resistance alone is a huge upgrade, but a better display, stereo speakers, A10 fusion, better cameras, faster wireless, better battery etc. are pretty great upgrades imo (and don't forget the 3GB of RAM in the Plus).
That being said, the jump from the 7 to 8 doesn't seem as significant. It is faster, better cameras, True Tone could be nice etc. but some other upgrades from the 6s to 7 (water resistance, battery) aren't there. I would make an exception for wireless charging, but I don't believe that is supported out of the box; you need an accessory for it.