Clannad side stories has some beautiful and sexy art, I'll give it that. Some of the stories were adapted into the anime, and of course those were good. Of those stories that were good and weren't included in the anime, though, only a few come to mind. Mei Sunohara's story, Ryou Fujibayashi's story, and Akio Furukawa's story.
Mei has a nice prequel story about her brother in middle school. Ryou has a prequel story about being mistaken for Kyou and forced to play volleyball. And Akio has a cool prequel story about when and how he first got together with Sanae. I think these stories actually added to the value of the brand as a whole. The rest were kind of silly or already explained thoroughly enough in the anime to be redundant.
Ushio's story is just downright retarded. It's illegal to let a young child wander the globe on her own, she'd never make it past customs.
Fuko was really cute in virtually every scene she showed up in, which was seemingly every story.
The familiar voices and music and artwork certainly got me in the mood to rewatch all of Clannad again, so it really pulled at the heartstrings of nostalgia in that way. But was it really worth $18? Almost the same price as the full game itself, while being nowhere near as good. . .
Well, if you can afford it, it's definitely worth reading. Or in this case, listening to. If you can't afford it, you're missing out on Nagisa in a baseball outfit and Nagisa in a bath towel, images I will gladly take all the way to my grave. This concludes my 100% completion rate of Clannad, having played the original visual novel and Tomoyo After Story long since. My love of Clannad won't lose to anyone, so to me, this purchase was a necessity, side story or not.
Now there's just 9 visual novels on my to-do list, but Da Capo III is almost fully translated and edited by Mangagamer, so it'll be back to ten again in no time.