I already own the spoonplugging book by Buck Perry and was wondering if buying the Lunkers Love Nightcrawlers book would be worth it, or if they're basically the same (in terms of structure fishing)? I'm talking specifically in terms of how they talk about structure fishing, not in regards to the other stuff (live bait fishing/spoonplugging)

Yes definitely Lunkers love Nightcrawlers is a great book 

Recommend Nightcrawlers

There were two versions of LLN books, the original version published in 1972, and then an updated one in 1988. If you’re only interested in the structure aspect, Perry’s book is the “bible” in that regard. That said, if you’re interested in structure presented in a slightly more modern way, along with any of the other stuff (tackle, sonar, maps, cover, fancy diagrams, etc.), then just pick up a copy of the “updated” version. Done that way, there would be no need for the 1972 edition.