It may, in fact, be a waste of some time for the boards, but they have changed several things about PBL tests from the time that you took them. One is the addition of anatomy/histo/embryo questions to your second year tests, in addition to the normal case and topic questions. If you don't read the histo, you'll be lost, IMO.
Additionaly, some people can survive perfectly well for two years memorizing high yield facts. I'm just not one of them. I do look at the high yield stuff in order to determine which things I should spend more time on-- and that's it. I've seen too many people,though, that relied heavily on it in my class. That's part of the reason why we started with 162 people and now have 153. They fell by the wayside. Be careful with how much time you spend on it.