Can't recall if I posted in this specific 7 vs. 7 Plus thread, so I'll share anyway. Two years ago, when I jumped from the 5 to the 6, it felt ENORMOUS. After two years of the 6 and 6S, it feels normal - if not small - in my hand. I was really, really hoping for some major visual changes to the 7 series but we didn't quite get that. That's the reason I first started to consider getting the 7+ - going from a 6S to a 7+ would certainly create that change I was craving.
Before I committed to the Plus, I went to the VZW store and compared my 6S to the larger model. Honestly...after having a 6 and 6S for two years, the 6S Plus realllllly didn't feel that much bigger. In fact, it felt kinda nice. The extra keyboard real estate felt great, screen size was super easy on the eyes. I'm not mad about the additional battery life and I certainly won't be mad about the 1080p screen res. And, of course, the camera is a massive perk. I document my entire life through pictures on Instagram. I've also taken to offloading my pictures every few months and creating digital albums kinda like my parents had done for us when we were little, just with physical pictures. Haha. So, the upgraded camera is really valuable to me.
Worst case scenario, on the slim chance that I HATE it, I have it for a year. I swap it out next year for a smaller model. Or, if I'm that desperate, I sell it and grab a 7. I don't think it will come to that, though - the pluses significantly outweigh the negatives here. No pun intended.
EDIT: In regards to one-handing it, I'm not really able to efficiently one-hand my 6S right now so that isn't something I will miss. It's not an application I use very often.