Without knowing what you are producing and require, that's difficult to answer. If your output is WebHelp, then maybe the fact that it will not work very well if at all in modern browsers might help.
Take a look at the RoboHelp Tour on my site. That lists all the changed and new features for each version. From that you can pick the ones relevant to you.
See www.grainge.org for RoboHelp and Authoring information