First of all, we should note that there was a vibrant black culture before the black power movement came into existence in the 1960s. We should not imply that there was some lack of culture in the African American community. Therefore, it might be better to ask how the black power movement changed black culture.
What the black power movement did was to create a new aspect of black culture, one that was aggressive in asserting its "blackness" its "soul." This was a culture that was made by blacks for blacks, not for white consumption.
With the black power movement came an effort to be more "African" in culture. This was when African clothing started to become popular among African Americans. This was when hair was worn "natural" (in "Afros"). This was when the Black Arts movement arose with people like Amiri Baraka. This was the time when Black Studies departments started to spring up in higher education.
So, it is not really right to imply that the black power movement made black culture better or richer, but rather that it changed black culture, injecting a more nationalistic strain into that culture.