> I cannot imagine your spacecraft is getting safer because of outdated hardware.()
Given the possibility of hardware bugs; eg FOOF, Intel dev bug, outdated hardware is well tested hardware, and as such, is arguably safer than newer, less-well tested hardware.
I doubt there's a material difference in well-testedness in hardware from the 70s/80s vs hardware from, say, the early 00s. Certainly, don't incorporate brand new off-the-shelf commercial hardware designed in 2019 for such a task, but a 15-20 year lag should give you similar (if not better) reliability than a 30-40 year lag.
Given the possibility of hardware bugs; eg FOOF, Intel dev bug, outdated hardware is well tested hardware, and as such, is arguably safer than newer, less-well tested hardware.