I thought for sure I'd come in here and find that someone had posted a solution:

After redeeming the GM code from the Mac Dev Center in the App Store, a message is displayed:

OS X v10.9 is already installed on this computer. Use the Updates page to install the 10.9 update or if you would like to download the full OS X installer click Continue.

The last developer preview of Mavericks was build 13A584, GM is build 13A598. However, using the App Store to check for updates returns no updates available (well, iPhoto, iTunes, and Command Line Tools have been updated today, but no Mavericks update).

It seems like I'll have to download the full (5.29 GB) setup image (bigger than a DVD, I don't think that was the case with 10.8?) to update to this release..