That's a very good question! I buy a cel for the 
artwork on it. I don't care if I haven't seen the 
show yet. There are anime shows I like a lot, 
like Big O, that I probably won't have a cel of, 
because the artwork and style of the individual 
cels are so simple that the very few that would 
interest me are, in my opinion, too expensive.

I buy cels primarily for the art on it, although 
I have noticed that many others buy cels 
primarily for the character on it. I don't buy 
cels for an investment, although that's the 
excuse I give to my spouse, who isn't fooled 
because he knows I'll never sell any of the more 
expensive ones anyway...