I didn't as I'm still waiting for my game but for what I've gathered so far, they're not exactly worth it.
I heard the characters in the DLC are not in any way more powerful or useful than the ones available. Also they don't have any kind of new scenes to see nor they contribute for getting trophies.
I personally wouldn't get this DLC.
As for Atelier Meruru, the japanese game has DLC but that is an awesome and huge dungeon, full of enemies, items to get and new bosses. I've seen a playthrough of that and that one looks like a great deal. If something similar were to be released for Totori I'd go for it, but just these characters with nothing more, I wouldn't.