The ability to mimic not only people but technology to perfection would probably allow Changeling individuals to rule worlds the way vampires and other clever immortals gain world dominance in mainstream fantasy writing. All it takes is a bit of patience, a bit of sense of drama, and a string of really mysterious deaths...
That's a good point. Changelings wouldn't need their own "stuff," they can aquire it pretty easily from others. They seem to do the most damage when they are quietly infiltrating.