I understand your concerns about "pigeon-holing" yourself, but my opinion is that if you are really serious about pursuing NICU, doing a preceptorship there is the best way to get your foot in the door. NICU is so different from any other area of nursing. And if you make a good impression, you may even be able to get a job in the NICU that you precept in. It's such a good way to have an "in" that many other new grads do not! You will need to consider how seriously you want to pursue NICU, or if you could be equally happy working with adults in med-surg or ICU. For me, once I knew that I wanted to do NICU, it was hard to even consider the prospect of working with adults again!
I am a new grad, and will start my job as a NICU nurse in June. I went all in, took a risk, and only applied to NICUs (but I applied just about everywhere in the state because I didn't care about moving). It worked out well for me! My favorite things about NICU?
-Knowing that I'll never have to throw out my back trying to move one of my patients up in bed
-When one of your tiniest babies grabs your finger in an attempt to stop you from doing whatever is irritating him (assessment, diaper change)...like it could make a difference
-The reaction from people when you tell them you are a NICU nurse
-When the parents of a baby who were too afraid to visit because they weren't sure he would make it, come in and hold him for the first time.