Siri, which I use multiple times per day. It's incredibly useful and much faster than typing, and the 2x processing power. The iPhone 4 was still noticeably slow, the iPhone 5 is more than fast enough.
The new iPhone S/C is basically a cheaply made (The 5S is not cheaply made, it uses the same grade material as the iPhone 5)iPhone 5 with a few more bells and whistles.
Literally, the S models are EXACTLY what you just defined them as.
iPhone 3GS introduced to the iPhone family an immensely faster processor, a better camera, updated, more efficient internals, and a new feature: video recording.
The iPhone 4S introduced to the iPhone family an immensely faster processor, a better camera, updated, more efficient internals and a new feature: Siri.
The iPhone 5S not only introduced an EXTREMELY faster processor, but also an all new Co-processor and made the jump to 64 bit. They also didn't just introduce a new camera, but added in an all new detailed imaging process software and new camera features like Slo-Mo video, zooming during videos, and burst shot. In addition to updated, more efficient internals, they also introduced a new feature: Touch ID.
If anything the iPhone 5S is the most detailed S update. Out of every S update this brings the newest features.
As far as the 5C, yes, it's just an iPhone 5 with cheaper materials to bring the cost down some, but also adds a slightly better battery.