I also have poor spatial memory (especially when it comes to navigating), but the book recommends using a place you're extremely comfortable with as your memory palace. I used the second house I grew up in for the first memory task (a to-do list). After a few times walking through the house and seeing the hilarious images I've placed in each room, not only do I remember the to-do list but I've enhanced my memory of my home. I can remember how the carpet felt, what the wall textures look like, and how it even smelled.
Best of luck to you; it's been really fun so far!
From what I gather reading the synopsis and the relevant discussion here: I'm not so sure how useful it would be for me. At the very least: I think it'd be a challenging technique for me to pick up.
It sounds like it relies on having a good spatial memory, e.g: being able to hold "maps" in your head. I've always been terrible at that, just ask anyone from my D&D campaigns.
However I think I'll pick up a copy of the book; even if I can't apply the techniques it really piqued my interest.