Niche Books, How To Sell & Find Niche Books (?) And Correct Genre & Sub-Genre Placement

I am basically regurgitating what I posted today in response to a thread on Kindleboards, but, I wanted to share my thoughts here, as they are very relevant to how I write. So I've cleaned it up (typing long passages for forum responses on your iPhone is really difficult, btw,) and away we go....
I do not consider extreme use of a story element niche (more violence, more sex). Nor do I consider