Kimber is NOT known for producing a quality magazine. Nuff said on that.
Again, unless you're storing your ammo in an unsealed container, outside, exposed to a daily watering from the sprinklers, left lying in the hot sun, AND run over by the mower on occasion, your ammo isn't going to go "bad." The bullet and primer form a tight seal and it's very unlikely that any moisture will ever penetrate.
The normal indication of a mag spring going bad is the last one or two rounds fail to feed. The springs are incredibly durable, it's the repeditive loading and unloading that causes them to weaken--not storage compression--and unless you're a compeditive shooter firing hundreds a rounds a month, it's unlikely that you'll wear out the mag springs. Mags springs, like light bulbs, do have a lifespan. But just because a bulb exceeds its specified hours and still glows doesn't mean it has to be changed. Mag springs are good until not.
If mag spring wear is a concern, or you don't trust the condition of the ones you have, Wolff Springs has them starting at about $8+shp. Change them out once a year if you feel they are weak; at that price it's a no-brainer.