In a Georgia NICU Level 3 30 bed NICU I worked in there were 2 LPNs who had been working there for nearly 20 years. They were not transferred to Peds or Mother-Baby Unit but were only allowed to care for feeders & growers. Our policy was that if they left, they would only be rehired if they had their RN. Any new nurses hired into the NICU were to be RNs or RN students in their second year of nursing school.
There are only RNs in the the NICU here in my new town in Alabama which is a Level 3, 25 bed unit.
Both of these hospitals hire LPNs to work in their Mother-Baby Units and Post-partum and Well Baby Nursery. (One hospital has a mother-baby unit where post-partum and well baby nursery are essentially combined and the other is the old-fashioned separated way.)
So, luvbug, this very non-scientific poll here at allnurses neonatal nursing board seems to confirm your suspicions that an RN degree is probably needed if you want to work in a busy NICU. In smaller towns I'd expect you'd have a much better chance of working with babies either in a nursery or in L&D, but I'd bet they'd be healthy babies and any really sick or preemie ones would be shipped away to a larger hospital which is equipped to deal with such illnesses and preemie needs.
Good luck and please visit us here often!!!