[adhesive_wombat]

90 degree turns don't "wear out" as such, it's usually more that they (might) produce a reflection in a high-speed line. This is why high-speed traces are often curved. Also 90-degree corners can concentrate mechanical stress and act as acid traps which affect manufacturability. They're also ugly (and I'm only half joking).

Power-up failure of a PCB is far more likely to be due to inrush current burning something out or thermal cycling leading to a broken connection than a viscous-current effect.

Also, space-based devices aren't always cold: it actually takes a lot of engineering to keep them from overheating unless they're in perpetual shade, and even then you need to do more work to get to a superconductive regime.