Several years ago I used Aperture and ended up switching to LR4, but miss a few of the features of Aperture. I am trying to figure out a way of using Aperture to access some of my master files without having to duplicate my master files from LR4. It is my understanding that if I import files into Aperture that the images go into a specific Aperture Library. What I really liked about LR was that my master files could sit where ever I wanted them and the application only accessed the files rather than stowed the masters into a unique application library.
You can import images into Aperture as referenced originals, and reference them in their original location, without moving them into the aperture library. Only you must not move them, rename them, edit them in any way after importing them into Aperture, for that will break the connection between the version in Aperture and the referenced original master.