It's wasteful if it sits on your shelf and you don't read it. If you read at night like we're supposed to and you're learning, and it expands your knowledge base and ability to treat patients, it's not a waste.
Every resident should have their seminal specialty text on hand. Whether it's about reading up on a particular syndrome, diagnosis, or the like after the day's work, or using it for PRITE review or board specialty exam....
The K&S edition is relatively new, so it should last at least until the end of your residency.
Despite the constant screaming, we're also prescribing a lot of the same meds that we did 20 years ago. So a psychopharm text isn't a bad investment in my opinion either. In fact, it's those meds that really require a good understanding. You certainly don't want to be limited to SSRIs and atypicals. I'm not saying you need the large 2000 page psychopharm text, but a good psychopharm text is essential to have in some form.
Besides, the OP was referring to their book stipend, which certainly takes the sting out of the purchasing process.