I recently threw out my racking cane, it was turning cloudy and there was a piece of trub stuck in it that I couldn't get out for the life of me.
I remember the lady at a LHBS telling me you should replace all plastic components (even buckets) every six months, but this particular shop always pushes unneeded merchandise.
I'm thinking buckets can be used indefinitely, or at least while they're in good shape. And transfer stuff can be used as long as they don't taste bad since by the time you use them, you should be mostly out of fermentables.