I think it depends on how you use your knife.
-I bought a Mini Grip for a family member who has used it as his only EDC for close to 4 years without any trouble with the springs. He uses his knife like a normal person and only opens it when he needs to cut something.
-On the other hand, I am an habitual knifesterbater and have broken the springs on one Grip, two Mini Grips and a 530. I have a habit of repeatedly opening the knife I am carrying while watching TV, driving, etc. The springs work great when used normally but don't stand up to the extra wear and tear that I put on a knife.
The average knife user shouldn't have any reservations about the service life of the springs. If a spring should break, Benchmade will fix it for you.