I don't think it's fair to say that Chinese users aren't missing a lot. At the end of the day, a small number of users are responsible for the overwhelming majority of quality content created and discovered (authorship and curation). Those users more often than not rely on high quality content irrespective of national origin. When you cut off that access for those people, it's certain to limit the quality, breadth and depth of what they create and share with their peers in China.

I expect this to be especially true with Twitter, which is often a very valuable back channel for many communities of interest (for example, a lot of prominent engineers in several programming language communities use Twitter as a way to share novel ideas and libraries).

When you cut off Chinese users from these sites, you cut them off from a lot more than just inconvenient political content.