You've sent me back to Solti's recording to compare your judgment to my memories and present perception. Spot-listening, I like it a bit more than you do.
Though not a fan of Fischer-D's ventures into heldenbariton territory - or even of his voice in general - I have to say, listening again, that I like him more than I did originally, and that his eloquence in Amfortas's monologues overcomes my reservations. I can't recall any singer finding such a wealth of nuance in the words and music, and he supplies an exemplary legato line as well. These are virtues of a great Lieder singer, and I'm much moved by what I hear. As with F-D's Gunther in the Solti Gotterdammerung, Amfortas emerges as noble but also oversensitive and weak - exactly the character Wagner gives us.
Zoltan Kelemen is another singer who hasn't the vocal fulness and heft of such great predecessors as Hermann Uhde and Gustav Neidlinger, but I have to say that his Klingsor is very effectively neurotic, perverse rather than merely nasty, making good use of a voice that's naturally brittle and edgy. Good character casting, reminiscent of Gerhard Stolze's Mime.
It was Kollo's rather colorless, unheroic voice that was for me the main disappointment of the recording. Listening now, I still find it so. He's an intelligent artist, and his intentions are good; he just needs more voice. I might prefer him to Peter Hoffmann, who, together with the mediocre Dunja Vejzovic (sp?) makes Karajan's cast, to my mind, more seriously flawed than Solti's. A weakish Parsifal is a liability, but a weakish Parsifal and a dismal Kundry together pretty much screw the whole second act.
Solti's major failing is in shaping and sustaining momentum over Wagner's long, conversational passages. That can be felt here, but where there's a clearly marked formal structure, e.g., in the temple scene and orchestral passages, he does nicely. The Vienna Philharmonic and choirs play and sing splendidly, and Decca's engineering fully captures the beauty of the score.