I think "Louse Detective" had a couple of good examples of one reason the show is less funny now: the writers no longer know when to quit.
The Tom Brokaw thing was funny. And then he said that dumbass "greatest regeneration" line, and suddenly it wasn't funny. If they couldn't think of a decent line, they should have quit while they were ahead.
And I had a hearty laugh at Moe's line about the pickle jar. It was a good gag. But again, the writers go too far with the pictures of Moe and the pickle jar, which not only added nothing to the gag, but actually sucked the humor out of the gag. Suddenly, the thing I had just been laughing at seemed completely unfunny.
Note to the writers: when the gag is over, STOP!
I don't ever remember them doing that in the first eight seasons or so. In fact, in the early seasons, I can't remember a single gag that just fell completely flat.
And it's not as if I'm *that* difficult to please; I thought the "he liked hookers" joke was amusing.