I've got four of the Pioneer CS-R500's that I bought new in 1971 or so and have had in continous service since then. I have found them to be a very nice speaker and a pleasure to listen too, but they do have some definite characteristics that might not appeal to everyone. They are definitely one of the old style "West Coast sound" speakers and sound great on Rock & Roll, Jazz, Blues, etc., but really aren't the best choice for Classical music.
They can also be painfully bright when driven by modern solid state (SS) gear, like my Sony TA-F45 or my Yamaha CA-400II integrated amps, but very nice sounding on vintage SS gear like my Pioneer SX-680 or Kenwood KR-6340 receivers. They also sound wonderful on tubes as I was surprised to learn when I paired mine up for a short time with McIntosh MC30 tube amps.
So, in my experience, they should be driven with at least 45w/ch. when paired with SS gear to get the best out of them. As mentioned before, they did sound great on my Mac tube amps (30w/ch.), but were definitely underdriven when paired with my Pioneer SX-626 (27w/ch.).
You don't mention what the rest of your system is, but if your one working speaker sounds good on your electronics and the "West Coast sound" is compatible with your favorite music, I would definitely spend the time and trouble to get them refurbished and operating as they should. I think you would be pleased with the result. Enjoy!