Instead of include complete replacements such as a media player or file manager I would allow the possibility to uninstall default applications so anyone can decide what to use in any case.
I would also like to see improvements and new features on the existing applications, not only bug fixes. See, for example, the work that has been done to Hildon or Ovi Maps, maybe not all the patches are safe enough to be included with the CSSU some of them could be included when they prove to be tested enough.