1. Far better AF
2. Far better DR (really malleable files, reminds me more of K5 at ISO80 but this time at FF and 36mp)
3. Pixel Shift - is worth it
4. Astro tracer - The many times I struggled to keep ISO/Shutter speed/aperture within reasonable limits on cameras before this.
5. Wifi - splendid! for shooting in really odd angles (like camera on the floor, shooting the ceiling)
6. Build quality of the camera just feels nice holding it.
7. Shallow DOF look that is easier with a FF
8. Shooting groups of ppl with less distortion using the K24/2.8 vs using my DA15ltd.
9. Easier working distances for portraits that need more subject isolation
All worth it.
Furthermore, its nice to think that my friends paid a bit more and got a less feature packed camera with the D610 and D800.