I've been listening to a few of the Knas on YT to start my search, and one thing I've discovered is that Act 1 is a perfect cure for insomnia. I'm always looking for music to fall asleep by and this is it, especially with Kna conducting. Of course, this is a very pleasant way to fall asleep, so no problems there. The only potential problem is coming up against singers that don't satisfy you or irritate you, since you're quite sensitive in the early hours.
My list of "yes but..." singers unfortunately starts with Martha Modl and since she's on most of the Knas that's serious. I totally love Regine Crespin - my favourite Kundry - and there are two of the Knas with her in the role, 1958 and 1960. Unfortunately the performances don't have quite the electricity of Kna's best years and some of the other singers aren't at their absolute best. Ah well....
I need to hear the Karajan in full - not on YT, and neither is the 1964 Vickers. I don't know about Solti - I like his Meistersinger and Gotterdammerung but ideally I'm after something more spiritual. I'm also less of a fan of Kubelik than many others - I never warmed to his Meistersinger for instance and his conducting stays largely earthbound for me.
For now I'm trying to sort out the many Knas. The 1951 and 1962 are pretty much as good as they are always made out to be, and the good stereo sound in 1962 is a big bonus.
Talking about people who have written about Parsifal, have you read Mark Twain?
"The first act of the three occupied two hours, and I enjoyed that in spite of the singing. [...] it seems to me that the chief virtue in song is melody, air, tune, rhythm, or what you please to call it, and that when this feature is absent what remains is a picture with the color left out. I was not able to detect in the vocal parts of "Parsifal" anything that might with confidence be called rhythm or tune or melody; one person performed at a time--and a long time, too--often in a noble, and always in a high-toned, voice; but he only pulled out long notes, then some short ones, then another long one, then a sharp, quick, peremptory bark or two--and so on and so on; and when he was done you saw that the information which he had conveyed had not compensated for the disturbance. [...] An ignorant person gets tired of listening to gymnastic intervals in the long run, no matter how pleasant they may be. In "Parsifal" there is a hermit named Gurnemanz who stands on the stage in one spot and practices by the hour, while first one and then another character of the cast endures what he can of it and then retires to die".