As far as I can see, you can't import to a new catalogue from an old CO catalogue. You can from a lightroom catalogue etc.
The solution I have come up with though is very similar. I am exporting from the old catalogue originals with included edits. I am then importing these into a new catalogue.
I have altered my workflow slightly as a result.
For each session I have a folder with sub folders 'captures', 'selects', 'output' (processed jpg) and now I have added 'edits'. This folder contains the selected Raw files exported with edits. So, I can always bring them into a new catalogue.
I'm doing this as I've had a few occurrences of catalogues being corrupted so I am building a workflow to defend myself against that.
Jonathan