I tend to agree with this person. The matching 
pencil, b/g & whatever does enhance the cel.  
Anime cels are not art pieces signed by the 
artist, but to me the pencil is the unknown 
artist's signature that should remain with the 
cel.  I do understand the dilema here, I have 
cels that the pencil alone takes my eye away from 
the paint.  Tough call!  Hate to even suggest you 
consider keeping a color copy instead.  I do not 
know what I would do?  Good Luck with your 
decision :-).