Do you go through them all to the toe? If they are at that stage, probably best to bin. I don't bother resoling anymore, but when I used to I found that you could keep the shoe pretty much as good as new provided you stopped wearing as soon as the some went through (need some self-discipline and a new pair waiting in the wings!), but if the rand needed replacing it probably wasn't worth it, as the characteristics of the shoe changed somewhat.