In the past I upgraded every cycle, but this phone 'does enough' for me to keep it.

First: I hate that Apple has moved ENTIRELY to a gesture based interface and removed the home button on the new phones.

I liked the home button, and I dread the day when I have to upgrade my mother's phone and explain to her how to use the phone without a psychical button- it will probably never be the same for her.

Also my use of "apps" has stayed nearly level in the past 3 years.
I have my thermostat app, my Podcast app, Twitter, Nike Run Club, my bank, Weather Underground, Google Music, Scrabble, and my SecureToken from work.

I feel these apps all ran well enough on the iPhone 5 - the processing power is almost entirely irrelevant to me now.

And the camera is pretty good for snaps. Google's Night Shot feature is sorely lacking on iPhone but other than that I get good enough photos.

I don't see how they're going to get existing users to upgrade as fast as they used to - they aren't.

My warranty runs out on the phone next month - the reason to upgrade will be when it is damaged enough where the repair cost is too high for me to be comfortable with.

Or if they dramatically improve the camera - but it would have to be dramatic.