I don't know about layout/genga/douga sets, 
because I'm pretty sure I wouldn't know a 
slightly or moderately incomplete set from a 
complete one.  Still don't know everything that's 
involved in anime production.  But I can answer 
on the cel "scene completion", because I've 
gotten that urge myself along the way, and picked 
up multiple cels from a single scene.  I've never 
managed to complete one, though.  And, then I've 
let go of a couple of cels from these sequences, 
when stronger lusts...ur, inclinations took hold.

But if you're confessing to any type of 
obsessiveness, yes, you're in one of the right 
hobbies to express it!  Just remember that the 
rest of us can probably match (or surpass) you in 
obsessiveness, so always make your approach 
politely, and don't be devastated if and when 
your request gets turned down.  

Now - speaking of completionism - do I have to 
also post this message to the other two copies of 
your message?