I do it to my cel scans too. But tt's becoz my 
scanner doesn't do justice to them. It often 
comes up too dark so I haf to increase the 
brightness and contrast juz so it'll look more 
like my cel. In fact, when I do tt, I have the 
cel beside me to refer to. Anyway, tt is all i 
do, nothing else. 
But then, I thik there's a need to draw the line 
when it comes to over-beautifying the images. I 
haf had cases when the cel does not look as the 
gd as the image on the website and I can't help 
but feel a trifle cheated. Maybe you can really 
retouch the scans in your display gallery, as 
long as u dun intend to sell any...