What about the Media Set report which shows the usage of all the tapes, number of hard errors, number of mounts, amount of data written to them etc.
You could use the number of mounts as a metric, eg replace the tape after it has been mounted 50 times, though I'd also say that if the tape has been used less times than that but you are receiving hardware errors then it should also be replaced (note that software errors can be caused by various things so aren't very helpful as a useful metric).