@ptbcomposer : on the AppStore, at least, there's more booksale than app sales. And among apps, what's selling the most is "books" apps. In fact those are apps with only text, or text with a few effects.
So the market is good for that kind of stuff.
I'm working on that kind of things, so if you want to ask some questions, go for it !
In the end, what's the most important, if you want to make sales (it's not the same if you only want an artistic outcome, the work isn't the same) : marketing. Marketing, marketing, marketing, marketing !
With that, you can have great sales figures with an "average" game, but without coverage (marketing), an awesome game won't do any sale...