WIT, you're making this more complicated than it is. Mostly, you want to keep your calories in check. There's no magic formula about how much nuts you can eat. You can eat relatively more nuts, and less of everything else; or relatively less nuts, and more of everything else, as long as the calories add up to around the same thing.
Nuts are useful in a few ways. They're packed with beneficial nutrients, they're very satiating (at least to most people) so they can help you keep from snacking on bad stuff, and it appears that people who eat nuts are generally thinner than those that don't, for possibly a few reasons.
For me, aside from absolutely loving nuts, I find they are the only thing that effectively fights off my one weakness -- bread and potato chip cravings. When I eat too many, I start gaining weight (good if I'm trying to gain; bad if I'm not :) ). But "too many" depends on the rest of my diet, not some magic formula