Before I rebuttal this post, I just want to make a disclaimer that I love the first 2 1/2 seasons of SpongeBob.
I'll sort of give you this one; SpongeBob is a very original concept in more ways than one, while The Simpsons has a very familiar premise. However, I would argue that the ideas they make with the premise are just as important (if not more so) as the premise itself. It's not really fair to say, "Oh it stars a family; we've seen that before, therefore it sucks!" I need some clarification here. Are you saying the golden period of The Simpsons reused jokes and plotlines? Because it didn't. In the grand scheme of 20 seasons, sure, but in the first eight or nine years, I was amazed how they managed to keep it fresh. And outside of a few catchphrases, the show didn't recycle jokes either. Maybe compared to SpongeBob, but there are some bits and pieces of good facial expressions throughout the series, and even some cartoonier moments once in a while (watch Treehouse of Horror IV and V if you don't believe me). And besides, I'm of the philosophy that a cartoon's writing is just as important as its artwork. If a show has great animation but unfunny jokes and bad writing, what's the point? (I'm not suggesting SpongeBob IS this way; I'm just speaking hypothetically)