Obviously it all comes down to personal preference and individual needs.
I say 'needs' because for the majority of people the upgrade from 5 to 5S is more of a 'want'. Ultimately, we all have to decide if this want is worth the cost.
However, in my case the move from 5 to 5S is more of a necessity. I'm surprised nobody has mentioned this, but I travel abroad quite often and I need the extra built-in wireless bands in the iPhone 5S.
To me, that alone justifies the upgrade. The 5S now supports more bands than any other iPhone, making it the first true "world" iPhone. If I'm paying for a 4G-capable iPhone, why would I want to limit myself to no 4G every time I go to Europe?
That's why I'm switching from iPhone 5 to 5S. The new camera, processor, and other enhancements are nice upgrades, as well.