Hi Anne,
As you may already know, if you upload the new version it will overwrite the older version. Updating child themes in most cases aren’t really necessary since it’s mostly just design updates rather than functionality. All of the functionality is featured inside the Genesis Framework. I wouldn’t worry about updating all of your sites to the newest version if you’re fine with how your sites currently look (Unless you have an easy way to transfer all of your customizations over to the new Theme).
This new version of Optimal is almost like owning an entirely brand new theme, but with the same layout and a few extra widget locations. The widget locations are labeled different to be consistent with standard Genesis Practices. For example, on the older versions the widgets were labeled Home Feature 1, Home Middle Wide, Welcome Area, etc etc. Now the widget locations are labeled Front Page 1, Front Page 2, Front Page 3, etc. to be more consistent.
As mentioned earlier, if you’re fine with how your sites look with the older version of Optimal, then I wouldn’t worry about updating to the new version…..Unless you really want the new look and feel, and if you have your customizations setup to be easily transferred.
If you have an example site that I can take a look at, then I can see how much effort it would take to make the jump.