One thing that sometimes makes me cautious of using older versions is not being entirely sure what the differences between them are. Of course I could just install the latest version and find out (assuming they actually include a change log -- it seems that not all packages do) but that's kind of messy and in some cases can even be dangerous if the new version damages my system, installs spyware, etc.
So for the packages that still include it why not include a link to the latest version of the change log text file on the page for each piece of software? For the software packages that stopped updating a public change log at some point you could post the last one that was released and create a forum (or perhaps just a topic in this forum which you would directly link to) where people can discuss what they think the changes are from version to version and how different versions have affected them.