In the grand scheme of things we COULD all go several years between phone upgrades.
For me though, I decided to break out of the shackles of the phone company, bite the bullet and just buy an iPhone at the full retail price.
Each year, I buy the newest and best phone, this year I bought the iPhone 7 Plus 256Gb in Jet Black. But I was able to sell my 6S Plus for well over half what I paid for it. So the price of upgrading to the new phone was a few hundred bucks. No contract, no hassles, no begging permission from my phone company.
The new iPhone is $969. I'd be shocked if I couldn't sell it for north of $500 when the next iPhone comes out. Perhaps more.
So is $300-$400 worth it for an entire year of a brand new phone, and more importantly an amazing camera (I travel a lot and so a good phone camera is worth it to me). Yeah, for me it is. I probably could have gotten the 128Gb model and saved a little more, but the cost of correcting that mistake down the road is pretty high, so I'd rather pay the extra up front there.