I always run studs in winter and have since the winter of 88.
My experience has been that the studs always wear out before the tires are worn out and that is the deal. I just get rid of them at that point. Shops will not re-stud them. It's way too much trouble to do it yourself because you will loose them at speed.
If you are careful and avoid spinning your tires they will last quite a long time. I bought a set for a teenage son and the studs were gone before the first winter was over. (Last time I did that!) I have gotten four seasons out of a set of studs.

I have also learned that there is a big difference in performance (traction,) between studded tires and have been unable to determine what makes one great and another mediocre. But I have had some (just by chance,) that made me feel invincible and I could drive at normal speeds over ice and snow. Others, like the ones I have now, are not a whole lot better than regular snow tires except for stopping on ice.

Anyone have any hot tips on how to judge the performance of these things before putting out the cash and learning the hard way????