I just hope the millions of people who upgraded to the 5S wont come back next year hating Apple and themselves for not being able to get the upgrade price..
It's no problem- sell the 5S and you'll be golden. BUT... if the 6 does come with a bigger screen, I would imagine that resale value would be lower. Did that happen with 4S to 5?
I can't say what my next phone will be, but if the next one is an iPhone, I'm sticking to the S models. I like the S models and 2/3 iPhones I've owned were S models. And if fits into my 2yr contract timeline. And I think the S has more substantial upgrades- a new design is nice with some extra features, but Touch ID, the camera and iOS 7, while sounding like minor things, really, really are great features.
I think they will release an iPhone with a bigger screen.