I don't think anyone develops (neglects/does not neglect) their Fi. I think the best we can hope for is to develop how we use Fi, or any cognitive function. We can learn to fine tune its application including when not to let it drive our behavior and when it's appropriate to bring it into play.
Before I had even heard about cognitive functions like Fi, I was developing skills to fine tune my control over my Fi. By this, I mean that I had already identified a couple of flaws in myself that only later I would find out were Fi related. Then, I tried to work on these problems. I think this pattern of identifying maladaptive behaviors and then working on them is a sign of general maturity and wisdom. You don't need to understand hierarchies of cognitive functions to do this. But after I learned about Fi, whoa Nellie. I was able to identify my misuse of Fi with even more accuracy, and thus develop my finely tuned control of Fi even more.
In retrospect, I see that my Fi problems seemed to fall into two categories:
- Fi on overdrive - This is when I let my Fi impulses drive my behavior. I was over-indulging my Fi. For example, I had a very strong rebellious streak that vigorously fought against anything that I perceived was preventing me from being my true self. I didn't know that this was my Fi in overdrive, but in a way, I didn't need to know about Fi to know that my rebellious steak was causing me problems. It seemed out of balance and I knew I sometimes overreacted to perceived threats.
- Not using Fi enough - This is when I don't use my Fi to check my Ne. It seems like our secondary functions must ALWAYS be used to check the excesses of our dominant functions regardless of personality type. I also got myself into trouble by letting my Ne run amuck. Being Ne dominant, I love to take in new information. But sometimes, I take in new information at the expense of sorting and make judgments on the information I was taking in. This lead to all sorts of problems for me.
Neglecting vs. Not Neglecting Fi
The point of my post is that to neglect Fi is to not attend to how you are using it. To not neglect Fi is to be mindful of how it operates in your life and then to tweak how you let Fi drive your choices. When it comes to Fi mindfulness for ENFPs, I think the two problems I identified above are the areas that we need to be mindful of.
BTW, I did not mention it in this post, but another aspect of being mindful (or not neglecting) one's Fi, is understanding Fi's strengths and leveraging those strengths whenever possible.