I have many bookmarks. What is the easiest way to save them when going to a newer Opera version?
From which verison to which? If you just upgrade from for example version 29 to 30, you don't have to save them somewhere else. It's though recommended to take a back up of your bookmarks, and you can do that by simply copying the "Bookmarks" file in /home/username/.config/opera, and restore it if needed.
Believe in the 12 versions all bookmarks were lost. In the mid 20 Opera versions I think some carried over and some were lost. I think when I had both version 12.16 and version 28 together I just imported them from 12.16 to the higher 20s versions. But now with 30 it won't allow you to run 12.16 together in Ubuntu 14.04LTS. BTW you still can run both of those Opera versions together on Ubuntu 12.04.
One way I did save bookmarks in the past was copy and paste them all in a LibreOffice Writer file then email it to myself. But then you have to individually re-enter each one at a time which is a pain.
Looking for an easier way to save them.
did you try export them to HTML (from 12)?
and then import it in your O30..(O-menu>> more tools >> import bookmarks and settings>>...from HTML file in dropdowwn list)