It would be useful. For me if i log out and then log back in again then everything is reset back to default, don't know if that how its meant to be or a bug, or if it would work for you?
Also you could add remembering the expression object window size would be great, every time i open C3 its shrunk back to a tiny box, then i have to stretch it out again, which is a pain as the grab/resize handles don't register properly.