David Cretney wrote:should I capture it to the same archive on an external drive or should I create a new QR Archive?
Your choice!
As you observed, QRecall's data de-duplication means that capturing the new volume to your existing archive won't make it much bigger because most of the new volume is a copy of what's already been captured.
The question is really, do you want to keep the history of changes from your old system? If so, then keep the archive. You'll end up with an archive that has two volumes, which you can then use the Combine Items command to stitch into a single volume so you keep an unbroken history of your files.
If you really don't need that history, proceeding with a new archive makes for a clean start.
Enjoy!