Springs are stressed components and are designed for "infinite life." But this is only under ideal conditions like perfect steel, etc. Any small piece of junk in the steel, nick, or other defect will create a stress concentration which can result in a fatigue failure. Examine the failed...
Snug is all you need to do w/ the plastic version as well. Don't over torque it, use an appropriate cap wrench, and it's a forever part. Plus the thread dimensions/surface finish differences compared to the plastic version are a non issue if one doesn't swap. Not to mention the inner filter...
F=MA, so the higher the acceleration/deceleration, the higher the "Load" (Dynamic vs Static).
This applies to all G vectors, longitudinal, lateral, and vertical.