First of all I don't shoot Nikon, but I just upgraded my primary Pentax DSLR from a K10D (introduced 2006) to the K5. The 5100 and the K5 share the same sensor, while I can't speak to the individual camera, I will say that the new camera is like night and day compared to the old. The technology advancements are incredible. The lowlight ISO capability made all my lenses a stop or two faster. The ability to individually adjust the fine autofocus for every lens (up to 20) on the Pentax, in-camera HDR, video, etc. That's not to say my K10's (of which I own two) aren't great cameras and produce great images, but as I said, the advancements since 2006 (your camera was introduced in 2005) have blown me away. I would not have said that prior to receiving and using the new camera. I thought it would be incremental, but I was wrong. The ability of the camera far outweighs my capability! It was a much steeper learning curve than I anticipated. If you owned a D90, I probably would say wait awhile but since you are using 6 year old technology I would consider upgrading.