My bookshelf is a scary place to go. There are all genres of books, yet they all have similar themes. The Greeks once said that there are only seven, count 'em seven, true stories. Everything else is just a mix of those.
It makes me think of Italian food. So many of the dishes are unique yet they are all based on the same/similar core of ingredients.
So I'm looking at my ideas as a place to mix and match yet feel familiar enough that it will appeal to more than just me.