I don't think it is about paying more for a cel 
with a sketch for me but certain cels I wouldn't 
buy without a skietch.  There is a Sailor Moon 
cel on yahoo japan right now that does not have a 
sketch and if it did I would but it.  I don't 
think I would pay much more but I don't really 
want the cel without the sketch. 

As for backgrounds I prefer if a cel has the 
matching background but not having a background 
isn't going to stop me from buyin a cel.  What I 
really hate is if a cel is shown with a 
mismatched background.  I think cels that are 
shown with backgrounds that you can tell in a 
second are wrong look stupid.