Yesterday I posted two identical stories, except that one was illustrated, the other not.
The illustrated version had many more downloads. 4551 to 1243.
The illustrated version had a higher SOL adjusted score: 6.82 to 6.01 based on 61 votes as opposed to 11 votes.
Approximately 75% of the votes for the illustrated version were 8 or higher.
About 40% of the votes for the story without illustrations were 8 or higher.
So it seems readers are more inclined to download an illustrated story, and of those who vote, the illustrations increased the appeal of the story.
But of those who responded to me directly (four people), two preferred the illustrated story and two preferred the story without pictures.