I will have at least one cel restored soon here: 
http://www.srlabs.com/

The service is expensive (apparenty at least 
$200) but those people have been specialists for 
many years. You can ask them for a free kit of 
information about their works.

My opinion about restoration is that having a 
cel restored is a good thing from the moment you 
mention it clearly, say who made it (has to be a 
specialist, not an amateur) and when, and that 
the result is perfect. It is the only way to 
have a very nice cel from old series whose cels 
have line-fading.