well one thing that you can consider is the fact 
that when a type of collectible has a limited run 
it rises the price due to rarity right? Umm are 
they or are they not going to CG for most anime, 
and in the near forseeable future I think cels 
will be phased out very quickly. For the most 
part the shows we are scrambling to get cels from 
now are just about the last of the shows that 
will have cels. As such it'll be hard to say that 
anyone will forget the new classics Tenchi, 
Bebop, Lodoss, etc... these will be the only cels 
that are collected because that's all there will 
ever be! The only cels on the auction block will 
be from personal collections, so yes they will 
hold at least most of their value since no one 
will want to part with their precious precious 
cels!

hehehe This is the horror and the joy of cel 
collecting... personally I don't care about 
future value since I'm going to keep my very 
favorites (well at least one of each Washu I can 
get LOL)for as long as my cold dead fingers can 
keep them away from all of you people ROFLOL!

Charlie 
(I was j/k with that last line of course ;)