I am sure Hong Kong's situation is known to some people in mainland China, and there are a lot of mainlanders who in fact travel and study abroad. It's not just shopping. Also, they sometimes go through the firewall in order to have Internet access to what is happening. During the Umbrella Movement, I saw some mainlanders actually coming just to look at the situation for themselves. I asked them if they were worried, and they said they just wanted to take part in this. They actually recognized me, even though they were from the far north.
I am sure that if Hong Kong has universal suffrage and human rights respected, that also sends an important message to China, and I'm sure that is also one of the reasons why China is holding back on its promise to give us universal suffrage.