That's a very interesting analysis. It makes perfect sense.All of the real life Ni doms and Ni secondaries I know have issues with insomnia.
I could go into a long dissertation about how the N functions are centered in the Cingulate system, which is the mental switchboard that can never shut off, but the simple answer is that Ni is tied to the parts of the mind responsible for dreaming. Therefore, the part of our minds that should take over when sleeping are already operating while we are awake, making it very difficult for us to get to sleep.
The end result is feeling like we can never shut our minds off.
Some of my Ne friends have exhibited insomnia issues, but they seem to be able to nap and catch up on their sleep much better than the Ni users I know, but I couldn't verify which type is more likely to suffer from insomnia (he posted at 5am).
It's one of the side effects to balance the amazing insights of N.