If you have cels professionally framed with UV 
glass there is nothing to fear (not counting 
natural disasters). Sunlight cannot fade lines 
and there isn't much else that could harm the cel 
unless it is close to a dart board or something. 
The copy idea is interesting, I actually 
considered doing that so I could scan some of my 
oversized cels without distortion by getting it 
copied smaller. The truth is, no copy of any kind 
is ever as good looking as the actual cel. Having 
it under UV glass is just like having it in a cel 
book. My only suggestion is to not put it over a 
heater or radiator.

So long,
    Larg0