I'm the same, I've always found the '72 Japan shows to be uninspiring...to me, the US 72 tour marked the last stage of my favorite Zeppelin period.
The US 72 tour was, for me, the last time the whole band was on fire; sure, after that you had some amazing individual performances but I can't think of a single show post US 72 that I'd take over their earlier live shows. Page and Bonham were great in Europe 73 but Plant's voice from late 72 onwards always let them down in my eyes. I'm not one to wax lyrical over Earls Court for example, as I find Robert's vocals to be too hit and miss (and Page too sloppy) for me to be able to really enjoy the shows.