D750, should I send in for shutter recall or not?

But to the OP, if your current shutter is fine, this confirms our point that if it ain't broke, don't fix it. A replacement is not necessarily better if your current shutter is fine and the actuation count is not super high.

Totally agree with this, esp if the owner and camera will be dependent on Nikon USA for the service (they tend to have a really unpredictable track record: many repairs go flawlessly, but enough go sideways that I wouldn't think of sending an item in unless it was within warranty and showing blindingly obvious problems with blindingly obvious solutions that even the most overworked, undertrained tech and communications staff could reasonably be expected not to screw up).

Issues serious enough for Nikon to acknowledge generally manifest early on in the life of the camera: historically (and counter-intuitively), the less clicks your shutter has seen the more likely it would have displayed the documented potential problems already if it had them. The fact you have experienced zero shutter issues since 2014, with a sporadically used camera, means you're unlikely to suddenly have glitches develop now or two years from now.

"Leave well enough alone" is my hard-won philosophy with anything Nikon. Yes, you might get a new, guaranteed problem-free shutter. But theres also a good chance Nikon could permanently destabilize your camera with minor or significant recurring issues it never had before you sent it in. Having owned many pieces of Nikon gear since the 1980s (bodies, lenses, scanners), and dealt with Nikon Melville several times, I would personally not send in a camera that had been trouble-free for six years just because Nikon is offering a free part upgrade. Left unmolested, your D750 will probably continue on for another three or four years just fine (by which point it will be fully depreciated and you'll be looking to replace it anyway).