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This is (at best) worthless advice grossly contaminated by inverted causality & confirmation/survivorship bias. http://www.niaid.nih.gov/grants-contracts/find-your-niche
First, you dont search for & "find" yr niche. Yr niche finds you.
Second, of course if you look at successful grant awardees, they'll have a "niche". Do the unsuccessful not have a niche?
Third, years of steady funding are what develop yr ideas into an actual research program: yr "niche".
I could keep enumerating more ways in which this whole idea is completely backwards.
You MUST, however, take whatever you've actually got to substantively support yr grant application & CHARACTERIZE it as yr "niche".
That is, you need to convince reviewerz that what yr proposing is unique, important & you are uniquely positioned to pursue it.
You don't "find" a niche except over multiple years trajectory of funded research activities, so "find yr niche" is worthless grant advice.
But as grant writing strategy, you CONSTRUCT yr niche out of whatever raw material you've got in yr possession: data, expertise, etc.
Yr "niche" is a constructed sales tool, not a thing you actually seek & find.
