I never really heard of "nappy" being used in a positive context except within natural hair communities and that has been very recent..like within the last 5 years.
But every since I can recall I've always heard the term "nappy" be used negatively. I honestly believe that is still how the majority of people see the term.
I also think there is a difference in the term "nappy" and "kinky". When I was growing up "nappy" meant hair that is very tangled and is uncombed and was always seen as bad. Kinky just meant hair that is either naturally tightly coiled or highly textured hair that isn't curly or wavy. Given, depending on the person the term "kinky" could be perceived as good or bad. But "nappy" was always negative period..didn't matter what kind of hair it was referring to at all.