It's funny how fads come and go, I could point to each decade I've played and find something a bassist just couldn't live without, until of course the next fad happened. chorus pedals, pointy basses, headless basses, badass bridge, biamped rig, active bass, midi, the lists go on and on. But we had to be current and that's what it took.
Right now the current fad is a passive p bass and a micro amp, at least on talk bass. Who's knows what the next "must have" will be. But I guarantee, most will have to get it.
To answer the question of my most useless fad? The sanded back of the neck.
I ruined a nice p bass neck back in the day by removing all the finish off the back of the neck. The reality was it didn't make the bass any faster or more comfortable to play. These days a sanded neck feels fast at first, but play it for any length of time and your hand will polish it back to a gloss feel, and is just as fast.