Ni/Se: Make the best (Ni) of what you've got (Se).
Ne/Si: The things we've got are not the best (Si), how do we make them better (Ne)?
Does this sound rightish?
That seems like a decent simplification.
Ni-ers incorporate novelty by finding new ways to look at (and thus new impressions to garner from) the details of the present moment. Ne-ers incorporate novelty by finding new ways to change the present moment so it differs from past experience.
Coming up with this right now I see it more as (but I'm also taking this more from Socionics so I don't know how much this applies in MBTI)
Ni/Se --> Contemplative/Action - Ni is studious of concepts and information and synthesizing them into what makes sense and is passive. Se is putting what Ni learns into action and is non-passive. So it's as if an INTJ might spend a lot of time determining what is going on behind a system of occurrences and once they know what is going on they act on it with Se.
Si/Ne --> Experience/PossibleExperience - Si maximizes the experience and enjoyment of what already is. Ne comes up with ideas on how to better or have more fun with Si. Like how an ENTP might come up with an idea on how to fly and try to make it happen so he/she can enjoy the idea and experience.