I have 157000 miles now in my car and did not replace the idler pulley when I replaced the serpentine belt. I'm afraid if I'm going for a long drive, it could get me stuck on the side of the road due to that. I would think it's not a waste of money. it's better to replace it now than get stranded somewhere and pay a huge amount for towing.
Great write-up. I'm thinking about doing this in the near future and was wondering how many people also replace the idler pulleys when replacing the serpentine belt. What are the indications that a pulley should be replaced? Is it a waste of time/money to do this preemptively?