are blackness and whiteness useful concepts in the study of popular music?

In a word, no.
Blackness and whiteness within popular music is neither here nor there. Looking back over the years we can see our fair share of both ‘genres’. In the 50s and 60s artists like Elvis Presley or The Beatles famously covered music that was considered ‘black’, listeners were often just unaware of this because the ‘white’ covers were more commonly played on radio. Russell Potter (1999) said with music genres crossing over it is harder to define than ever, which is very true and proves why blackness and whiteness are not useful concepts. While some styles of music may be more ‘black’ or more ‘white’, it is impossible to know whether or not that is the case. Musical style can be inspired from all sorts of cultures and races. Eminem is a good example of a mixture of both. While he is a white man, the sound  and style of his music could be considered ‘black’, so if we were to use the blackness and whiteness concepts - where would he fit?

Does the emergence of the digital download signal the end for the music industry?

There are a number of events and changes that occurred within the music industry that caused the availability of digital downloads. In the 90’s german research company Fraunhofer claimed that their compression format would reduce the bit rate of digital audio without a loss in quality, this reduction in file size means that the MP3 is born. Until the birth of the MP3 it wasn’t possible to distribute digital audio over the internet, so while this new technology is a step forward it also comes with a big negative - piracy.
Websites like Napster, where people worldwide can share and get music for free brings problems to the music industry. 

Lessig suggests file sharing can be broken down into four main groups; substitute for purchasing, sampling before buying, gaining access to copyrighted music no longer available or to access non-copyrighted material. This suggests peoples reasons for downloading music should be accounted for however only one from the four is damaging and illegal to the industry. This confirms that piracy is not a signal for the end of the music industry. 

Can popular music ever really achieve political change?

There are a number of songs that have political influences within the lyrics or the music itself but whether or not they ever achieve influencing those political views on the general public is another story.  

Take for example Billy Holidays infamous song ‘Strange Fruit’. This song, which is essentially about the lynching of black people, was at first denied to the general public and wasn’t released because of its content and strong political influences. This song had the groundwork to politically shake the world at the time but restrictions prevented this.

Another example is the 1988 ‘Acid Rave’ stories that tainted the music thousands of teens listened to and resulted in laws being passed to prevent raves or similar kinds of music being produced. This explains how big of an impact music with political influences can make however, Longhurst notes that “in approaching the politics of popular music we need to address not only the context of it lyrics but also the sound and reception in particular contexts”. Music can only ever really cause political awareness rather than change and the circumstances in which it is used effects how influential it is.