I really identify with what you said about 
the "perfect" cel, by common definition..
I will say right now, in all frankness, that most 
of the "perfect A " cels, with exact centering, 
character facing forward with neutral 
expression...the "perfect" cels people always 
talk about...bore the heck out of me.  One might 
say that it's due to my financial situation--I'm 
not overflowing with cash, and these are usually 
among the most expensive, but if given the choice 
between one of these, and a cel that's 
less "perfect," with some element of action, I'd 
take the latter.  Even if the price was the same.
I've got several cels in my collection that cost 
me over $100 (and one which cost me several times 
that much ^_^;;) but if I took my top 5 favorite 
cels, I don't think there's a one I spent more 
than $50 on in that number.  Most of my 
favourites cost me less than $30.  And that's not 
just because I feel better about how much I spent 
on them. ;)  They're just the ones I love most, 
for the scene and character, and sometimes 
additional meaning (yeah, I know I rant about 
Guitar way too much, but my first cel of him 
remains my favourite cel to this day--I think I 
got it from Nick for about $15.)
I realize my tastes will change, and I'll no 
longer be interested in collecting cels, so I'll 
stop buying some day.  But I've found that many 
of my other interests of the past which I no 
longer pursue still have enough meaning to me 
that I keep the things I had--I just don't get 
more.  As such, I think my cels will hold a place 
in my heart for a very long time, even if I stop 
buying new ones.  That's what justifies it for 
me.  I know it'll last, and they give me that 
giddy-geeky-glee in the meantime. ^-^
Err...and disjointed as this response is..  I 
never find myself considering resale value in the 
cels I get..  I get them because I want them, and 
hope to keep them.  There are some I feel I might 
part with now (the change of interest, especially 
in cases when I purchased a cel on a whim,) but 
it was never the plan.  I *won't* buy a cel 
that's grossly overpriced, though, simply because 
I figure I can find one later on that's just as 
nice, and less expensive.  And if not, that money 
can go to something else I'll probably enjoy just 
as much.
I ramble so much. ^-^;;  Apologies.

~Mala