Not just rationalizations — there are actually good reasons to upgrade your phone sooner rather than later.
- The new phone will be in warranty.
- Flash drives slow down over time.
- Batteries degrade over time.
- Buttons wear out. Probably on all phones, but in particular, the home button and sleep/wake buttons on iPhones seem to wear out a lot as you hit the two-year mark.
- You will be able to run the newest OSs and apps well.
- If you're on a plan where your phone is subsidized and your monthly payment doesn't go down once it's paid off, you're leaving money on the table if you don't take advantage of the ability to upgrade as soon as it's possible.
- iPhones hold their value well, and you'll get more money for it the sooner you sell it.
So... if you can afford to upgrade comfortably, do it!