It seems like most people who visit Kanchanaburi are either Thai, backpackers, or on a day trip from elsewhere in the region (generally in a tour bus). The region is beautiful though, and if you enjoy nature and history I think it’s well worth taking a couple of days to explore the area.
Kanchanaburi is infamous for being the nexus of the Thailand-Burma Railway during World War II (if you’ve seen Bridge on the River Kwai this is the setting). Along those lines, and given the short shrift given to the Pacific Theater in the American educational system, we all read The Railway Man on the trip, which provided some useful historical context and interesting discussion topics. I understand the movie of the same name is a bit graphic, but the book was appropriate enough for teens.