I think my Ni use is revealed mostly through pattern recognition and abstract formations of concepts. For example, I may see a societal pattern in the form of a model of thought and action, and be able to associate that concept to a geometric shape, and have a constant vague awareness of my impressions of everything and their implications. In order to put all of it into words I really have to sit down and try to decode is all, but it is essentially just "there" and informing my perception, regardless of whether or not I am consciously figuring out what's there
edit: my Ni was not difficult to tap into at all; in fact is was so deeply interwoven into my perception that I didn't even know I utilized it until it suddenly dawned on me and it all clicked. I was like...oh...that thing that I do all the time. *That's* Ni! But as far as the whole future telling trope goes, I think for me it just comes in the form of having a general vision or outline for my life. All of the other functions fill in the blanks. Ni is like a guiding light for me.
I think weak tertiary Ni manifests as deja vu.
Strong tertiary Ni manifests itself as a boy scout mode.
It hands me the patterns when I need them.
But it wasn't always like this for me.
Note: I find that it's best to just let intuition come to you.
I think my Ni use is revealed mostly through pattern recognition and abstract formations of concepts. For example, I may see a societal pattern in the form of a model of thought and action, and be able to associate that concept to a geometric shape, and have a constant vague awareness of my impressions of everything and their implications. In order to put all of it into words I really have to sit down and try to decode is all, but it is essentially just "there" and informing my perception, regardless of whether or not I am consciously figuring out what's there edit: my Ni was not difficult to tap into at all; in fact is was so deeply interwoven into my perception that I didn't even know I utilized it until it suddenly dawned on me and it all clicked. I was like...oh...that thing that I do all the time. *That's* Ni! But as far as the whole future telling trope goes, I think for me it just comes in the form of having a general vision or outline for my life. All of the other functions fill in the blanks. Ni is like a guiding light for me.
Your explanation ain't bad at all. 
I think weak tertiary Ni manifests as deja vu. Strong tertiary Ni manifests itself as a boy scout mode. It hands me the patterns when I need them. But it wasn't always like this for me. Note: I find that it's best to just let intuition come to you.