This is how I see it.
In a few years, will much of this stuff be relevant if you watch it on re-run? Older, standalone episodes are the ones where I can watch at any time and laugh while they're also playing off some real life aspects at the time.
Just last night I watched the re-run where the boys built the ladder to heaven to see Kenny because of a ticket to the candy shop and it turned into Japan trying to out-do them and beat them there, and then staging their whole thing. Thoroughly enjoyed re-watching that one. That and the ****** (city) wall for the Mongolians and kidnappers. There were references to real life happenings at the time but it didn't dominate the entire episode or season and makes it so much easier to watch, even all these years after it originally aired.
You nailed it imo. I'd actually say this season and last season are two of the weakest if not the two weakest in recent memory. Like you said, in 10 years if you flip a random rerun of SP on and it's the mongolians episode, it stands on its own and you'll probably enjoy it in the same way one could enjoy a random episode of Star Trek TOS or TNG randomly, as each episode is it's own story and stands on its own.
If you flip it on only to see one of the weaker episodes in this season or previous, it'll just be one small part of an on-going storyline you likely won't even fully remember. I'm not denying each episode has had its moments but I much prefer the standalone eps where each one had its own story.
I know I'll get crucified here for saying this, but I was never really even a big fan of the multi part episodes they did in the past, and I know I'm in the minority much like I am with these two seasons.
I'm also not nearly as big a fan of PC principal as many people are either. I feel like if he were treated like other characters that are the focal point of an episode now and then rather than for a full season, I'd like his schtick a lot more. But when I'm subjected to him for 12 straight episodes it loses its magic with me.