I've got a pair of speakers that are over 30 years old that work just fine today. While they have "pleated" surrounds, the rubber surrounds on the Castles will be fine. Still not sure that's the best bang for the buck, but I totally relate to your motivations.
Also, I have owned the earlier Quad 12L. I found them very clean, slightly warm, with an excellent clean, "quiet" tweeter. I also found, compared to several other speakers I had, the midrange did not "open up" in the room like the others did. Not sure if the newer 12L2s or the 21L2s have this trait, but I would a-b compare the Quad sound to other contenders. Good luck.
Also, I have owned the earlier Quad 12L. I found them very clean, slightly warm, with an excellent clean, "quiet" tweeter. I also found, compared to several other speakers I had, the midrange did not "open up" in the room like the others did. Not sure if the newer 12L2s or the 21L2s have this trait, but I would a-b compare the Quad sound to other contenders. Good luck.