I usually go with the /trade/ philosophy. If you 
look at your cel collection and say,  I would 
rather have that cel than the money I could sell 
it for, then its a keeper. Or, further, if you 
would rather have what that money could buy, then 
its like trading. Trading cels for DVDs, or on 
and on. Its rather strange, but it usually works 
pretty well for me in deciding if I want to keep 
something or not, or if I want to keep collecting 
it. Like collectible card games. Man, I used to 
collect those! But then, I decided that I would 
rather have that energy in cels. I still have 
lots of my cards, but I don't buy any new ones.