> computer hardware which is unlikely to be reused and will historically need to be replaced every 24-36 months

That seems unreasonably short. My work computer is 10 years old (which is admittedly the other extreme, and far past the lifecycle policy, but it does what I need it to do and I just never really think about replacing it).

> My work computer is 10 years old... but it does what I need it to do and I just never really think about replacing it

It depends what you're working on. My work laptop is 5 years old, and it takes ~4 minutes to do a clean compile of a codebase I work on regularly. The laptop I had before that (which would now be around 10 years old) would take ~40 minutes to compile to the same codebase. It would be completely untenable for me to do the job I do with that laptop (and indeed I only started working in the area I do once I got this one).