I can see Ni-Te and Ni-Fe being impractical, but Fi-Ne and Ti-Ne might be even more useless. They become more valuable when Si has time to develop. During this period is when INXPs become truly adept in formulating ideas and making insightful connections. INTJs and INFJs seem to be late bloomers, and intuitives in general, but INFPs and INTPs are on a whole other level as far as I can tell. INFPs and INTPs are in my opinion the most capable of coming up with ideas that alter the course of society in unexpected ways, but the slowest to produce anything meaningful with their time. I'm speaking very generally and based on my observations again, just to be clear.
Ni/Ne and Si/Se are the 'absorption' functions. Therefore, INFJ and INTJ are very good at absorbing certain abstract information and making sense of it. I don't think Ni is paradoxical at all. It's just reading into a level of abstraction as opposed to something more concrete, aka Si. Ni gives INXJs more direction than INXPs, I think. INXJs are a lot likely to be happier working within existing frameworks and systems.
Ti and Fi are the deep thinking functions. INXPs create their own internal systems through constant, unending analysis and value that over 'what is'. Ni doms (and Si doms) by definition and functionality, do not prioritize their own analysis. They are perceivers first. Despite being Js, INXJs are actually more open minded to new information and perspectives than INXPs. INXPs are the judgers. Ti and Fi are categorising, labeling, sorting everything they encounter through their unique Ti or Fi lens, first and foremost. INFPs or INTPs that have systems which are rooted in faulty perception, false truths, etc. will not go anywhere with their analysis and that's where it becomes so important for any type to recognise they have massive blind spots in their cognition and need to have healthy relationships with all kinds of people to fill in that hole.
Also, I think idealism was the wrong word to use. I would just disregard that part of my post entirely lol