Some manufacturers put small foam sheets in CD boxes to keep the discs from falling off the jewels. Over the years the foam degrades and sticks to the discs like hell. I have a few opera box sets that fell victim to this. Extremely hard to remove.
I'd never glue anything to the printed side of a CD!
I think of getting one as an emergency spare. My first Philips DVD player still works flawlessly, and CDs sound great on it, too. The better the hardware is, they longer they will last, and the less reading error correction software they have. A clean digital signal is the main thing about CD playback.