I sometimes wonder if this is Henry Ford's "if I asked people what they wanted, they'd have said a 'a faster horse'" objection.
The question is perhaps not "what do we buy today that we could 3D print instead", but "what objects/things don't exist today that _could_ with widespread and affordable 3D printing" (and the associated new 3D modelling software/libraries/new-techniques which make the idea->object process more accessable).
You nailed it on the head. Often times, with new technologies that are a step function jump, rather than an incremental improvement, people think "what would I do with it that I already do, but faster/cheaper/easier", rather than "what new things does it allow me to do that I couldn't do before?"
The latter question is the correct one to answer with something as weird and new (new to consumer/pro-sumer) as 3D printing.
i'd like to press a button, and print my dinner. saves me time cooking. bonus points if it printed the utensils, all once use - thrown away after using!
The question is perhaps not "what do we buy today that we could 3D print instead", but "what objects/things don't exist today that _could_ with widespread and affordable 3D printing" (and the associated new 3D modelling software/libraries/new-techniques which make the idea->object process more accessable).