Self designed very specific objects are where it's at regarding 3D Printing IMO. Once you get into the habit of realizing that you can print a part for you'll find yourself doing it again and again.

Examples I've designed and printed include:

• two bluetooth speakers. I'm getting ready to print my first subwoofer
• tons of replacement parts (parts for kids toys, replacement knobs for our stove as the oem ones are $50/pop, etc)
• wheels with TPU tread and pockets for bearings for a fold up wagon. We've used that to cart our two kids around for 3 years now

You also find yourself being more adventurous with modifying other things knowing you can print interface parts. For example, our outdoor table had a 1.5" hole for umbrellas. We wanted a larger umbrella, which requires a bigger hole, so I cut a portion of the metal center of the table out and made a plastic adapter. I've also done lampshades and a bunch of other odds/ends around the house.