Mike,
I don't remember seeing spacers either but let me say this:
If you look through the back window of my car, the seat backs lean in toward the console. It's enough that you can feel it.
I plan on adding spacers to the inside tracks of my car whenever I get time to level them out. I'd bet that it is the prupose of those spacers. I have some thick metal spacers from a few sets of Lil Red Express seats that I'll use.