I went from a 64GB 6+ to the 128GB 6S+. I take a lot of slow motion videos while I travel, especially in landscapes out West. No cloud in the world can reach me there and its a pain to be hit with storage limitations just as you line up that perfect sunset time-lapse. The new 4K capability wouldn't help me if I was already hitting the limit on the older 1080P camera.
I'm paying full price so price is $1,030 tax included. Ouch! But if it's worth it to double the 64gb then I will.
I already have a 128GB iPad Mini 4 so as soon as the SIM-free 6S+ was released I grabbed a 64GB one...from the online store so it's being made right now I guess.
6 years ago I bought the iPhone 3GS with 32GB capacity and as I just used my MacBook, there was no problem with space then either.
But that didn't have 4K video capabilities...