We estimate that about 30% of the pre 1999 instrument have a tolerable level of noise, especially once making music in a live situation. As a solo recording instrument, the number might be higher.
I would say that if you have significant high frequency hearing loss, it might not be as dramatic to you.
Distillates, Spoilers, Elans, and Europas all have RF upgrades available. Europas tend to be the worst of that family and will be cured with an entirely new circuit. Distillates should probably be replaced with Europas because upgrading them is extremely tedious (read expensive) as they are completely hand-wired.