Ah. I didn't mean to get overtly critical or desire an accurate definition or anything. But doesn't worthwhile and meaningful mean the same thing? Something is worthwhile if it's meaningful and vice versa. It's circular reasoning. Is it not?
But Monogatari is also an exploration of the human condition. And it's also done well. So when you refer to the plot as worthless… But what is the plot of Monogatari? Are the arcs not set-up and ended properly?
Personally I think Monogatari and the aforementioned shows are all memorable, and therefore good. Whereas Sonny Boy is bad because it fails to leave an impression, any impression is a good impression, even if it's a bad impression. Even if it's one you don't necessarily prefer, it means you still got something out of it, hence worth. But that's just my reasoning.