I'd also be interested in someone knowledgeable weighing in on the quality of those books.

My first world problem with somewhat random information dumps like that is usually that I don't really find that it's a lack of resources holding you back from learning about certain topics, it's a lack of time. The quality of those books really has to significantly eclipse what's available on the internet (especially in terms of presentation of the material) before it seems worth buying them (to be fair, price is not a real issue here, just in principle). For instance, I don't really see the value of software reference manuals (unless you already know the software and just need the reference, but then you would likely own it already and not buy it from humble bundle, right?).