There is the concept of cumulative damage. About all of the comments on this thread have been reasonable. The thing to be aware of is that a highly stressed structural element such as a spoke may not have an infinite life. An individual spoke's actual life will be highly dependend on its individual history, which comes down to a complex synthesis of the peak stresses it has been subjected to, the amplitude of the stress variation from min to max, and the number of cycles it has undergone for various min to max stress levels. If you're confident that a given spoke has had an easy life in these terms, then it is a good candidate for re-use. If you're not confident, then you take your own risk.