Well, I have to echo what everyone else has said; 
repro cels lack the uniqueness and the direct tie 
to the anime that actual production cels have.

I'm also bothered by the "assembly line" aura of 
repro cels.  Not to sound pretentious, but they 
lack "art." Knowing that some poor, bored 
underpaid workers sat around painting the same 
areas with the same colors over and over and over 
again just seems to me to be the exact opposite 
of art.  Yes, they're "hand-painted," but to me 
it's like charging more for a house because the 
housepainters used brushes and rollers instead of 
spray-guns.  And then, to top it off, the 
background (if any) is always pre-printed.  

That being said though, I have to admit that some 
of those Evangelion repros look mighty tempting! 
O_o  Fortunately, I can't bring myself to pay 
that kind of money for them.