This is sort of an echo thread.
I very much agree with Dragon of Grief: we can't dodge the role the dollar sign plays in this whole process. SB continues to be a merchandising cash cow; his visage still commands economic attention.
It needs to be remembered that The Simpsons has encountered similar issues, where even the voice actors/actresses were expressing some level of misgiving regarding the decreasing quality of the writing. I am very curious to know what Tom Kenny et. al. think of the opinions being made here and likely elsewhere regarding seasons 4 and 5.
It also needs to be remembered that the writers almost completely changed after the movie. Most of the big names of seasons 2 and 3 (Walt Dohrn, CH Greenblatt, Kaz, Merriweather Williams, etc.) are no longer around. Most of the head writers (Casey Alexander, Luke Brookshier, Zeus Cervas, Dani Michaeli, Nate Cash, etc.) came in to replace them, and we only see a few of the old writers (Aaron Springer, Paul Tibbitt, and a couple others.)
The issue of ideas is likewise important. Of course season 1 was hardly bereft of new ideas, since many of the episodes (especially the early ones) dealt with our introduction to SB's predilections, from his love for the Krusty Krab to jellyfishing to blowing bubbles. The later episodes can't depend on that and have to find new ways to introduce those themes. A great example of this type of issue is the first season episode "Hooky." It's a great introduction to the characters' interaction with the air world above them, but there's no way you can repeat something like that. The idea was already taken in season 1, and the later seasons are thus left with less.
But even now, some of the episodes suggest to me that there are still many fresh ideas out there: take the episodes "Driven to Tears" and "Spy Buddies," for instance. They're both pretty good episodes, but they show that many unique approaches to the antics of SB and the other characters are still out there.
