Here's how I would use Lexile appropriately. Take Hemingway's "The Sun Also Rises." It has a low Lexile score because the sentences are all fairly short and simple (typical of Hemingway) and his vocabulary is also short and simple (also typical Hemingway).
As a teacher though, I also know that TSAR is an incredibly deep and complex book when it comes to the content and the ideas it contains. This would make it a GREAT book for a high school student who is reading below grade level - he would get to read a book that is suitable for his age, but within his reading comprehension range.
Similar thoughts for "The Grapes of Wrath" - the text itself is pretty straightforward, but I would NEVER give that book to an 8th grader - whereas the Hunger Games I could.
Conversely, just because a book has a high Lexile score does not mean it is just for upper level students. Depending on content, it may be appropriate for a younger student who is reading at a higher Lexile.
Another way I might use Lexile is this: Say I have a student in the 9th grade reading below grade level. He ought to be able to read things with a 1000L, but he's only reading at 775L.
To improve his reading comprehension, he needs to read text that is at or just above his current level- enough to challenge and grow but not leave him lost or overwhelmed. So I suggest The Hunger Games (810L). It will be challenging for him, but I know it's a high interest text- he will be motivated to keep reading even though it is difficult. A few months later, maybe we'll try a book at 850L, then 875L. By the end of the year, he won't be at grade level, but he'll be a LOT closer than if we hadn't help him gradually step up with high interest, appropriately leveled text.
I didn't know all this about Lexiles even a year ago. I've learned through exposure at Professional Developments, reading conferences and self-guided research. Parents who are worried about Lexile scores being used wrongly should be advocating for better professional development for their teachers and time for teachers to identify student's current reading levels and plan for reading remediation with Lexile measurements as one guide, NOT for removal of Lexile as a tool.