We had exactly the same problem, this is a SharePoint limitation due to the whole paradigm of independent sites. The best solution we could come up with was to create  (develop) a unified UI site  that shows information  from a specific data site (using a URL parameter telling it what site to show). This is not easy, but if you are careful, it can really make the management much easier

Another approach I've seen was to use/develop some kind of utility to copy changes from one site to all the other sites, not easy, as there are many possible changes you have to support.