Surely the viewpoint of value in upgrading is entirely dependant on a personal situation, as much as it is in the product itself?
A. If you're in the market to upgrade (end of contract, still on a 3GS/4/4S, have loadsamoney) then you'll see the strengths in the 5C and 5S phones, love the designs and the specs, etc.
B. If you're not wanting or able to upgrade (middle of contract on a 5, just got a 5, are skint) then you'll see the 5S/5C as a poor upgrade, with minimal benefits.
This is confirmation bias at work - the instinct to find evidence that supports your view, and exclude evidence that contradicts it.
There are some agreed truths...
- There is a strong desire to feel you have the latest or premium of Apple's products. [Hence the hate when the iPad 3 was quickly updated to the 4. The 3 still worked just the same, but the owners of the 3 lost that sense of owning the latest product.]
- The repeated comments about the 'S' cycle being only minor upgrades is of course nonsense. The greatest processor and graphics speed upratings have come with S models. Each S model has also had a camera improvement. And not just these number specs.. each S model has brought a significant feature. It's not the cosmetic redesign of the non-S models, admittedly, but not insignificant either.
- Everyone wants different things out of a phone. Some want features. Some want certain sizes. And some just want a phone! But what's right for one, is not right for another..
=> So, I would conclude that the 'S' iPhones are not "minor updates". I would conclude that how you perceive the latest iPhone will be influenced by what you currently own, what you would like to own, and what your financial situation is regarding being able to buy a new phone.