I used to believe that but I have heard from several people that their broken TBs looked new (except they were linear and not circular <G>). The only Miata timing belt I ever changed looked just like what I put it. If you had mixed them up behind your back and had me choose the old one I don't know if I could.

 

For someone who didn't want to do the work, I figured that was a fairly simple compromise. If it looked ragged then he'd probably do the job, if not- he'd go w/o.