Recommended settings for Specialized Brain with respect to durability
The threshold setup of your shock should have a negligible if not non-existent bearing on its longevity. Run it how you like it. 

To give you an idea of what you're concerned about breaking, watch this video that describes how Brain shocks work. About 2/3rds of the way through you will get to see the internals of a Brain shock's inertia valve. They are not as delicate as you may think.