Turns out this is easier than one could ever imagine. Open the Library you want to contain everything, use Finder to navigate to the Library you want to import/merge in, and simply drag-n-drop that Library into the open Aperture Library. You can see that and other cool tricks and feature descriptions on Apple’s Aperture Features page. It is a little out of date, but still an excellent reference.
Has it worked for you, Walter?
Would you still rebuild the the Library to be merged if it was from an EHD (say a trip shoot)?
Sounds like a nice short cut, will have to give it a try.
Stan
sbysshe.smugmug.com