Try going to “File” >> “Import Messages” and one of the options in the drop-down is “Import KMail Maildirs and Folder Structure”. I haven’t tried it myself, but it may be worth looking into.
I did it the way you tried and had success, but I also copied the relevant configuration files in ~/.kde4/share/config as well. Maybe that had something to do with it.
What you are seeing is just the index with none of the contents. As JumpingEarth says, you have to use Import which will add your old emails to a new set of folders to distinguish them from your current emails. It does work!
Your old KDE Kmail emails will have been in folders in ~/.kde/share/apps/kmail/mail (or ~/,kde4/etc if you have been using KDE4 already) labelled inbox, outbox, sent-mail etc.
If you have not saved these, the contents of your emails have gone.
Yes, that is what I meant. I don’t know if they are actually required, but I copied those 3 files (mostly because I didn’t want to re-enter account info), and it worked fine for me.
I had KDE 4.3 from factory installed on 11.1, though, so I was moving from (about) the same version of KMail on 11.1 to 11.2.