I've heard a lot of argument for and against rewelding a frame.... a trials rider at this bike shop I used to work at told me frames weren't rewelding because if it gets to the point of cracking... rewelding wont do much because the metal tubes in other spots of the frame have given in to stress enough to let that happen... so its just going to keep happening, cause your not fixing why it cracked... and it really doesn't buy you that much more time on a frame either...