Or, the good, the bad, and the as-yet-undecided.
While I've learned something from all my sources, some were more useful for their intended purposes than others.
The Good: I've currently found Lieber's book most useful for the NEG concepts and Mlodinow's for history. Both of them are not only informative, but also very entertaining. Lieber's poem-like typography is unique, but it her husband's whimsical (yet still perfectly relevant) illustrations that I enjoy best. Mlodinow, on the other hand, is a genius with words, with just the right mix of math, history, and humor-- yes, humor! And not the kind of garish comedy common nowadays, but educated, understated wit woven deftly in to augment and memorialize pivotal notions... There's a reason that book was the first to make it onto my list of favorites, and it's not because of its educational significance, though that is not to be overlooked either. All of the listed internet sources have been useful in some capacity, else I wouldn't have bothered to list them, though I have not explored any of them in full depth yet.
The Bad: However, it wasn't all sunshine, rainbows, and lollipops. Most of the online sources I found were either repeats of the same simple lessons over and over again or only tangentially related to my topic. It's not exactly a popular subject, so resources on NEG are limited, but still extensive enough for me to be unable to list all of the gobbledygook I encountered during my net wanderings. The gibberish of the old-fashioned books I obtained is, however, modest enough to all be recorded. My original tome by Harold Wolfe turned out to be exceedingly dull and a bit strangely organized, and while I had heard that H.P. Lovecraft's horror stories often incorporated NEG, I could only find one example of this, referring to its use in horrific architecture, which did not turn out to be useful at all.
And the As-Yet-Undecided: I am currently hoping Christopher Priests' Inverted World is more useful in the study of the use of NEG in fiction literature, though it is proving tricky to get a hold of, as are the other books I have not yet acquired (as evidenced by their un-acquired state).