I don't think that the disk can 'ware out' from playing it too much. I've got ridge racer and wipeout, wich were bought the day the psx was released over 5 years ago.
I must have played these for 1000's of gaming hours over the years and still play and look A1.
I would think that the CD drive unit might be starting to fade, they do ware out. like all things that are runned by a motor & electricty they will age and die (just like a motor car). Over the 5 years I've had and still got 3 Playstations and have renewed the CD Drive Unit on 2 of the at least twice.

Also I think I've still got those 12" black circular things with grooves on both sides and a hole in the middle. I think they were called L.P.'s or records. but they don't want to fit in my CD player.