I would think explaining how your clinicals went in those areas would help the person reading them understand why you would be a perfect fit. Put in your essay how passionate you are about being in the NICU. I'm not sure if you need to explain how this will help you achieve your long term goals once you graduate. When I was in school, that was something they wanted to know and basically was the letter itself. All you can do is your best and be honest about why you want to be there. I wish you all the best and I hope you get your first choice. Keep us posted.