I have to disagree with you on this point. I doubt Silk Road or people buying drugs online with bitcoins have affected the market for street drugs at all. Two completely different socio-economic markets.
Most who buy drugs in the inner city do not have access to bitcoin and/or Silk Road, and even if they did they would scoff at the inflated prices compared to the price on the streets.
From what I've read gangs where I live (Chicago), they don't get as involved in drug sales as one might think. It's less about drug territories and more about representing the block one grew up on. This American Life did a pretty good story about it in two episodes about a high school a couple of years ago.
Most who buy drugs in the inner city do not have access to bitcoin and/or Silk Road, and even if they did they would scoff at the inflated prices compared to the price on the streets.