How useful a 3D printer is depends entirely on how you use it. My recent projects were:

* Some prototype compressor wheels and housings for an RC vehicle

* Wargaming terrain

* A small enclosure for an oddly shaped LCD panel that I'm using as a dash in my racing sim rig

* A micro ATX PC case

They're useful if you've got complimentary hobbies, but if your reaction to a 3D printer is "I'd probably never use that", you're probably right. If you're not planning on designing your own parts, then mail order is fine for occasional use.