Hi Simone,
Thanks for sharing you glass polishing experiences. Look forward to hearing some more of your exploits.
I too had a similar moment to you, bought my first vintage digital watch - a Novus LED a few months ago and then just couldn't resist this for five pounds a few weeks later .....
Since then I've kind of been drawn more to the LCDs so they're the only two LEDs I've got.
Your faint calculator digits could be faded polarisers or less likely it could be a volt drop somewhere on the LCD drive signals. Probably the least invasive fix is going to be to put a thin film of polariser somehow between the inside of the glass window and the outside of the actual LCD display glass. I haven't had much luck finding small quantities of thin film yet but it is certainly produced.
Rgds,
MP.