I completly understand what you are going 
through.  Hell, I've been collecting stuff since 
I first had money to spend, so I've always had 
these same conflicts over something or other 
(remembers back to 9th grade when she spent about 
$300 to assemble the entire X-Men Ultra Fleer 
card set including all the chase cards)  The way 
I personally look at it is as a collectable, cels 
are something I can take with me to school 
because they don't take up too much space (unlike 
my Barbies), they pretty much retain thier value 
(unlike all the comics and action figures I've 
bought) and they are something I can have an 
online gallery of to share with others (unlike my 
*duck* Beanie Babies)  Since I still have one 
more year of undergrad, I don't really have any 
major expenses (though I should be saving some 
money for grad school and a car) and in fact, my 
spending on cels is motivating me to sell off a 
lot of other belongings.  And I know if I wasn't 
spending my money on cels, I'd be wasting it on 
something else that would be just as useless in 
practical life.  Of course I regret sometimes the 
amount of money I've put into them, but as long 
as I spend more time enjoying them then agonizing 
over them, I think continuing to collect them is 
well worth it.  And heck, as much as I want to go 
out and buy a ton more cels, I am thankfully 
restricted by my budget ^^;;