I have re-touched my cel scans in lots of cases.  
As far as damages such as faded lines or chipped 
paint- now, I don't digitally retouch them.  Like 
you, I like to scan my cels and present them as 
they are.

However, for the most part I retouch cel scans 
that have extreme dust problems.  As a fellow VOH 
collector, I'm sure you've noticed just how many 
cels from that show have an unimaginable amount 
of dust trapped inbetween cel layers- as well as 
times where the dust has actually permeated 
itself into the surface of the cel- making it 
near impossible to remove.  

Another scan I'm still retouching without much 
success is that one of Hard ( the one you have 
from the same sequence ) because of the dark 
colors and etc.  

For the most part, I really don't think you have 
to tell anyone that the cel has been re-touched 
to tone down the appearance of dust, etc. unless 
of course, you're selling the item or have it up 
for auction.