I like to keep mine as a set. If I liked the bg, 
would I separate the cel from the bg? If I liked 
the B layer to a three-unstuck-layer-setup, would 
I sell it as a two-layer setup?

I think that having the extras--- concept 
sketches, gengas, dougas, bgs, and so on--- are 
all wonderful additions to the cel itself, and 
that if you're lucky enough to have them in 
addition to the cel, that the whole is more 
important than the sum of its parts. They help 
provide a look into the creation process... and 
while the finished product that most people pay 
attention to is the cel, the rest of it helps 
provide a context. ^_^

Then again, I just love my sketches. :o)

I keep scans of the few things I've sold and the 
few things I've given away. If I really liked 
something I was getting rid of, someone had 
mentioned taking it to Kinko's. But I like 
the "whole" feeling of having as much as 
possible... and wouldn't feel good about 
separating the parts.

-Cres