There seems to be quite some overlap between NVC and I-messages [0], which are constructed in a similar manner:
1. I feel... (Insert feeling word) 2. when... (tell what caused the feeling). 3. I would like... (tell what you want to happen instead). (from [0])
I learnt about I-messages about 10 years ago in a seminar on conflict resolution and have tried to use them eversince. My personal impression is that they have really helped me - in solving conflicts, but also in growing as a person. Because, again purely subjective, my impression is that once you give others your I-messages, they are more likely to also respond with I-messages. Which again helps me to understand others and their needs better.
That said, NVC looks like a great addition, by making things more explicit with those four distinctions (observations vs. evaluations, etc.).