Hey!
So this is an actual question in community that a lot people are wondering about.
In my opinion - story doesn’t need to have art scenes for it to be a good story. This is an app for interactive story telling not novel style. The art scenes kinda makes it a novel style story and I have heard a lot people really dislike them and leave the story if they can’t skip it. Of course, no one will hit you if you include art scenes. 
A good alternative is character edits. A lot authors make custom poses that episode doesn’t have, making the story more interesting. I honestly like them better than art, but some art scenes just have their “charm”.
About spending money for art, you can check this discussion : )
P.S. I like to either draw by myself or try to look for anyone that’s looking for some practice and then get free art. : )