It would be great to see, what has been updated in newer templates compared to the one we have in place. Therefore it would be good to have all intermediate release notes accessible and probably (as the new "diff" for deployments) a diff for the template I have in place with the newer one.
So at the top of each template you will see "tv" - Tag Version and "tc" - Tag Comment.
The Tag Comment will tell you what was the most recent change to the template. We are currently building a release notification system for tags, so that you can see when tags have been added / changed.
Also of note some of the more popular templates, do have articles on the TLC, which you can read when an update is done.
As for being able to do a diff on your current template and the latest version, that is a very good idea, one which I have been meaning to implement. I will co-ordinate with Development team to see if we can get this released.