I went from the 4 to the 5S.
Totally worth it IMO. It's MUCH faster, LTE is amazing, the camera is great (120FPS video is cool too), the fingerprint scanner is amazing and works very well. Oddly enough it feels MUCH faster than the Galaxy S4 I had despite it being a 1.3GHz dual core instead of 1.9GHz quad.
The only downside is the battery life is worse. I used to be able to get 4-5 days off a single charge from my 4, but now I only get about 2 days from my 5S. It's still much better than the S4 that I had to plug in every night.
I'm really looking forward to the speed bump. Should be night and day over what I have now. I've also seen a couple of videos of the animation speed boost in iOS 7.1. Looks very speedy on the 5S. I can't see this being a bad purchase. I was happy with my 3G and my 4.