Being an author of work that provides several ways of understanding for multiple levels of readers, I believe that the sole reason people pick up anything to read is to be enlightened in one way or another.
Being an illustrator I demonstrate an insane and painful approach to the art of fine detail and being capable of drawing what I cannot express in words is something that can touch people in a different way.
That being said, I, for one, am extremely interested in glimpsing into the authors mind - say for example - that of Stephen King. His work made me want to know what he was like as a child, what he went through as an adult and the struggles and lifestyles he had. I have read his book "On Writing" and it is an incredible piece of work that has allowed me to love him more than I thought I could.
It is so interesting to know where an author comes from, and to be able to identify our similarities as well as our talents to spin pure magic with our words creates an important link that keeps us connected. To know the author well, and to know that there is a kindred human spirit typing those stories alongside us only enriches the experience of a piece of work.
The two arts, writing and illustrating are closely linked for me. Both avenues are intensive channels of expression that in no way could I achieve through my speech.
I think that a very high percentage of readers are searching for clues and plots and secrets as well as looking for a kindred personality within the words of a story (and a piece of art for that matter) and that when provided, you create a following of readers that loves to look forward to your style. It creates a sense of escapism that they cannot access in their "real life" and comes to be a portal of safety, imagination and possiblities that take them into places and personalities they would otherwise never meet.
Hopefully this answer not only illuminates my personal opinion on plot and characters but opens the way for others to validate their feelings on the importance of the two as well!
Love this question!
Have a great day :)