In my personal experience, every time I've gotten a new iPhone (only twice now, but still), I've been more over joyed with that purchase than almost any other purchase, save for experience purchases. I distinctly remember one year after buying my first iPhone (4S) thinking that it was arguably the best purchase I've ever made.
TBS, when I spend money on experiences (concerts, bars, trips, etc) I am much more happy than when I buy things (even the iPhone). People get off on different things, sometimes its just having the latest thing. If it provides you with happiness (even fleeting happiness), then so be it.
If you're happy with your 4S, and you don't believe the grass is greener on the other side, then by all means, I hope it brings you all the happiness you need.
In general, I've never been less than happy with a new Apple product, so I can understand just having faith that the iPhone 7 will be a great purchase. Even if it does fall short of what you're expecting, it can still be wondrous to own a new piece of technology like that.