I agree with both of the previous posts, and I truly enjoy your reference to reading between the lines as "soft corners." I want to reiterate that the average reader in reading any novel for the first time is looking for simple plot and character. Often we want to know about the "who" and the "what" the first time we read. It is the "where," "when," and most importantly "how," that are left to subsequent readings.
And, yes, foreshadowing is often left by the wayside as we hungrily search for the actual plot. Let me give you an example: Harry Potter and the Prisoner of Askaban. The first time I read this young adult novel, I was totally shocked (and disgusted, quite frankly) that Sirius Black turned out to be the good guy. I felt like the entire novel bled the idea that the guy was bad and then suddenly, in the shrieking shack, he turns out to be good? Balderdash! Then on subsequently reading the book to my children, I noticed all sorts of things that could have led me to the correct conclusion although, I'll admit, they are not meant to be obvious. I often like novels more the second and third time I read them as a result.
Just a little postscript for you, if it is a teacher reading a novel for the first time in order to teach it to the students, ... that teacher most likely will feel required to get deeper into the "where," "when" and "how"; therefore, when I am teaching a novel for the first time, it takes me forever to do my first reading as my mind goes into overload! Such is the bane of average intelligence, I suppose.
Often a reader misses what is not being said. If one reads any of the minimalists, such as Ernest Hemingway and Raymond Carver, the meanings below the surface are what are important.
Another aspect of a novel that many miss who are not familiar with an author is how much of the author is within his/her work. So knowing something of the author makes a significant difference in picking up on meanings and themes.
When we read a novel the first time, we often feel like something is important but we don't know for sure. Symbolism and foreshadowing are the most common things to miss, because you really can't truly appreciate them until you have read a book more than once. The only way to avoid this is to read books twice, or to read a summary and analysis before you read a book. Then, you won't miss important things because you will already know what's important.