I got way too familiar with the PSX CD drive, and I can't see any way that CD-Rs would wear the optical block faster than other discs. Certainly, if you're having severe read errors that cause the sled to re-zero, you'll be putting more wear on the sled. But, even if you're using a crappy CD-R that the PSX has trouble with, you won't get those errors often. Small read errors are re-tried with a tracking coil movement, not a sled movement, and that doesn't really wear out (it's always energized anyway as part of the tracking feedback). The laser power itself is controlled independent of the disc's characteristics, using a separate "mirror" sensor that just measures optical power at the laser diode (before reflecting off the disc).
If the disc is being read successfully, there's no possible way that a CD-R would put "more stress" on the drive than a normal disc. The laser maintains the same power and the same control loops are running regardless. The physical differences in the disc don't change the behavior of the drive - they just make the signal weaker coming back to the photosensors.