I know how you feel- fads are almost always 
hurtful for people who are into something because 
they truly like it, instead of because it's 
popular.  I remember several years ago when I was 
big time into the gothic scene, when it was 
something of an alternative culture, and then 
Marilyn Manson came along, and suddenly other 
bands became popular, the clothing became 
popular, coffee shops and dance clubs became 
popular.  The result was that the clothes became 
more expensive, concerts became more packed and 
the ticket prices went up, the clubs got so 
packed you couldn't dance, etc.  
The same thing happens when other things become 
popular, such as anime.  Because it is becoming 
so popular, the prices are going up- Tenchi and 
Fushigi Yugi cels are getting very popular and 
expensive, and also harder to find.  
I also notice other things about cel trends 
though- like other fads, the popularity tends to 
change and die down after a while.  I have an 
utena movie cel on ebay that hasn't even gotten 
an opening bid at $100 - and I know I've seen 
lesser cels for far more.  
I also notice that "who" you are matters- if Taro 
or some other sites carry the same cel as other 
places, people will buy from there but not from 
say, a private dealer.  I think there is some 
kind of prestige associated with it.  I saw some 
cels on ebay from the same sequences from some at 
Taro (and I am NOT picking on them, they do a 
good job and I had a happy dealing with them) go 
for far less but even that took several weeks, 
whereas taro's were gone in a few hours.