The object is to replace parts that have deteriorated. The pulleys deteriorate with usage, not with age. Save your money for the real problems.
I've recently had the same dilemma and opted to replace the pulleys at 90K. I also replaced the seals and in so doing punctured the A/C condenser = $300 fix!! No need to blow your wad right now and don't fix what ain't broken! It's not worth the risk.