Crap, mine had 148,000 miles on it and it still wasn't "gone". However, I think the wisdom is that the output starts to decline with age. These are, after all, mechanical potentiometers. There *is* a wearing surface. If your car is really old (mines 13 years and I finally replaced mine because I was doing my 60K service) but runs more or less fine, then it's up to whether you want to spend $30-$40 for a replacement TPS to hopefully optimize performance. If you're having some other problem that could be a TPS problem (there are some shoforum members who have had the TPS, even new ones, go bad. Ask Robby, centaurus3200) then the $30 is money well spent to try to solve the problem, IMO.
Rick