I've a slightly different interpretation of how N works. It does not seem to me that N is two different entities, Ne and Ni, but just N. The e/i is invoked based on whether the judging function is introverted or extroverted in attitude. I believe this in large part because even though I'm INTJ with very strong Ni and Te, my Fi is not weak, and when I use it, it invokes Ne (which is technically a shadow function), not Se. (It -can- and does work with my Se, but usually it's with Ne.)
So, the way to resolve the Ni/Ne "conflict" is really to resolve the Te/Fi conflict (which exists not only between the two individuals, but within each, as well). I can totally identify with ENFP and INFP feelings, and I think they sense that from me, but the conflict comes in because my Ni/Te will hop in and say, "You don't wanna do that. That would be really stupid." The (confirmation biased) experience of most INTJs is that Ni/Te logic is almost always right, and what we feel like doing is not something that we really want to do. The wise restraint of Ni Te overcomes the bold passion of Ne Fi.
Interestingly, this is what attracts ENFPs and INTJs together (and to a lesser degree, xNFPs and xNTJs in general). [Assuming male INTJ and female ENFP for pronoun and gender convenience.] The INTJ sees a beautiful and vibrant ENFP bringing an energy into his life that he enjoys: he has that same approach, inside, and it is this inner self that is joyously awakened by the ENFP. The ENFP, on the other hand, isn't attracted to the INTJ "logic" but rather the apparent imperturbability. She can emote and emote, and he'll just sit there, quietly enjoying the show. She can be herself, and he doesn't freak out: "Wow, he accepts me just as I am!" she thinks.
In other words, it is precisely the source of the attraction that becomes the source of the conflict. Ne Fi will always push for something more, and Ni Te will always restrain. It's a natural duality. They will always "conflict", but likewise, they need each other, because either extreme is bad. The trick is finding the equilibrium that allows both to be fully expressed.
Eventually, the combination will fail, if both people don't grow up a bit. (Which isn't saying much, really: immaturity will kill most relationships, regardless of the MBTI types involved.) In this case, the INTJ needs to learn for himself when more emotional spontaneity is appropriate, and the ENFP needs to learn when more careful planning is merited. And it isn't just about developing those weaker functions, it's about learning to accept and respect each other as is. The ENFP should allow the INTJ to be INTJ, most of the time, and the INTJ should similarly be careful not to unreasonably restrain the ENFP's natural enthusiasm.