This has now been confirmed by Connectix's Edward Jonathans, who provided me with some additional details: "Basically the Finder creates a resource if users have actually moved the SD8 control panel window. Altering settings within it alone does not produce the Updater problem, but moving the window's position and trying at any time to subsequently update produces the error. The updater does not look for this resource."
This has been fixed via a new Speed Doubler 8.0.1a Updater. If you already successfully updated with 8.0.1, you do not need this new version.
Meanwhile, if you do try the work-around for the original 8.0.1, be sure to move your Speed Doubler Preferences out of the System Folder before you remove the Speed Doubler software. Otherwise you will lose any Copy Agent or other customizations you may have made (advice that I found out about too late!).