The key series isn't always "more detailed" by design so much as the details get better with each model. The difference in the Key Series over earlier Precisions is in packaging. The Key's come in a box where you can see the tractor without unpacking it. The new packing is less expensive while being able to display the tractors without removing them from the box.
Also, the forthcoming 1066 open station will be offered in two configurations. The regular red/white, and the '77 model "black stripe". It is one sharp looking tractor in either config.
4020 Deere w/picker was available in a VERY limited gold plated version. They sell for megabucks. Also, 4020 nf was issued in a "Nashville Parts Expo" version, much more valuable than the regular 4020nf.
Next Deere Key is a model R, followed by a couple more that won't be 2-cylinders. That's all I know about them at this point.