Sometimes a negative finding can be useful.
I attempted on my character to skip one of the trait books, to see if I could save some gold. When I got to level 60, I bought the 2 gold book. It shows like you're ready for it, but it won't actually let you learn the book until you have read the lvl 40 1 gold book. *sigh*
Well, it was worth a shot. It did work in another game.
Incidentally, going without your trait book in pve/wvw doesn't feel at all gimpy, and now having the trait book my character really plays about the same.