What is your source ? It's lacking for me an effect on motivation.
I'm using NSI for almost a year. My initial side effects were pressure in the neck and forehead, a few days anxiety and a foggy brain. The foggy brain and muscle pains continued for a decent time (about four weeks).
Motivation was hightend to do sport: my condition became better (and I sported intensively before I took it) and I could do, without getting really tired, twice what I did normally. Social motivation on NSI is poor for me. I experience other people as flies around me and I'm more quick than ever to keep my distance.
So, it's important to note what kind of motivation is triggered when people say they are more motivated. Does it mean more energy, more pleasure, more social, more...? And maybe I had a long way to come, it took six till eight weeks before it worked properly and also effected the quality of my sleep.
Stress coping is much better and without NSI it gets really worse again. I tried 15, 25, 35, 40 mg and the best results came from 35 or 40. But that amount makes me non-social. Note: I'm really sensitive to medication, normally I don't take more than the minimal dose or I take lower. Because of the non-social effect, I'm trying NSI 25 mg with 5mg selegiline.
Cognitive: I see more connections between facts and information, my memory is better (and it should because stress is killing cognitive functions anyway and without stress it gets better. But I see a surplus given by NSI.) But this effect is minimal on 25 mg.
I hope this helps a bit.