I bought an iPhone 5S a while ago because of this, while I'd much rather have bought the iPhone 6. I really hope they come with a smaller model next time :-/. 3D Touch look useful.
(that said, I'm quite happy with the 5S. I don't have much need for what the 6 models offer.)
What's the line on force touch actually being useful vs. just hype? It's hard to resist the reality distortion field and not get excited from hearing about it, but I've been burned by the false promise of iPhone-S release cycles before ...
It's hard to say without using it, but the gut feeling I get from 3D Touch is that it will be very useful.
It strikes me as an innovation in the same category as the finger-no-stylus approach of the initial iPhone and, more recently, Touch ID. These features initially seem overhyped because they're such 'little' things, but because they affect your interaction with the device constantly, it'll be hard to live without once you're used to them.
(that said, I'm quite happy with the 5S. I don't have much need for what the 6 models offer.)