Well, I have very little advice to offer, but...
My game, The Moon Sliver, looks like this:
And to boot, it's a "walking simulator" with no voice acting, and a lot of reading. Yet it still managed to sell 17k copies so far, and get an average rating of 71% on Steam.
I didn't do anything special to market it, I literally just put it up on Steam, and happened to get a huge amount of exposure due to the sale that was occuring at the same time.
I think as long as you're honest and up front about what the game is in the description, and price it right, you won't have any trouble finding an audience. Don't worry too much about the graphical fidelity, or lack thereof.
I also agree with the poster that says they don't think niches are found, they're formed. So just try to get as many people to see it as possible, and you'll start finding that niche.
If you really have faith in the other elements--the gameplay, the story, etc--then mention them in the description. Maybe even relate a short version of the game's development story. I'm of the opinion that in indie gaming (especially now that Steam offers refunds), honesty is better than salesmanship.
Ok, I guess I had more advice to offer than I thought.
tl;dr
Just market to everyone, and be honest about what your product is, and you'll find your niche.