Same problem here with my old Mac 10.4.11 AppleWorks 6.2.9 files on my old MacMini...
and getting them into "Numbers (v3.2.2)" files.
This worked!
I still had Microsoft Excel 2008 (V12.3.6) for Mac on the "old MacMini".
I opened a blank Speadsheet in Microsoft Excel 2008 (V12.3.6);
I opened the AppleWorks 6.2.9 ".cwk spreadsheet, and then >select all >copy.
Then going to the blank spreadsheet in Microsoft Excel 2008 (V12.3.6),
I hit >Paste and then saved it as an ".xlsx" file.
I transferred that ".xlsx" file over to the New MacMini (OSX 10.9.5) desktop,
and opened Numbers (v3.2.2),
then >File >Open and navigated to the .xlsx file...
and Saved it as a ".numbers" file.
It worked, but Apple should respect "backward compatibility" for their faithful Mac users and
many of us that go back with their operating systems, firmware and software since day one,
and just make simple file transfers and backward compatibility much easier.
~Gene
http://geneleonemix.bandcamp.com/