You're right about the magnesium deficiency epidemic.
As far as nuts and seeds go, they are difficult to digest at all past the chewing stage. This is much different from the lab analysis that found high magnesium levels in the pumpkin seeds, where everything was completely chemically & mechanically broken down. Anyone who eats a lot of nuts/seeds has seen them in their stool (it's part of their "purpose" to not be digested well).
What I'm getting at is the "amount" of magnesium available in nuts/seeds is directly proportional to how well you chew them. It's also one major reason I don't eat too many nuts anymore, when I do it is in the form of nut butters.