For sure, entering a new anchorage at night can cause disorientation even with a plotter. In familiar anchorages we often get our bearings from familiar lights on shore. In a new anchorage, you don't have those familiar guide posts.
Regarding whether to preserve night vision or use a search light, the answer is- "sort of both."
When using the search light but try not to let the beam hit the mast or deck. The reflected light will ruin your night vision. Keep the beam out over the water so that only objects on the water reflect back. I really try to work with the ambient light though, looking for "contrast" on the water's surface. An overcast sky or a new moon can make that difficult though. Keep a hand near the shifter so that you can drop into neutral quickly if you spot a crab pot at the last second or hear one bumping along the hull.
As always, speed is a factor. Don't let fatigue push you into rushing into an anchorage in your desire to put the hook down and go to sleep. Go as slow as you have to, for as long as you have to.
You can practice by picking a nearby anchorage that you know is well marked and sailing there in the evening instead of daytime. Sometimes when cruising during a summer heat wave, I've opted to travel at night to spare myself the brutal heat and so I've arrived at night.