Ran across an ad for a Nismo multiple point wiring harness that ads more
ground points for a better running engine and electrical system.

Is this for real or a novalty item that's a waste of time and money ? I
can imagine that this kit would help the battery keep a charge
but I'm not so sure about horsepower gains and
increased gas mileage.

Higher torque in low and medium power bands.
Quicker throttle response and Stabilizes the engine at high RPM's.
Smoother Idling and improve starting.
Better fuel mileage with improved combustion.
Decrease of interfering stereo noises caused by insufficient grounding