Totally agree with you.  It seems that a norm of 
the collectors are under 25 and interest will 
change when you are only collecting briefly (few 
years) as priorities change.  Since we tend to 
collect on things we know about especially if a 
high price tag is at stake, it seems fair to say 
that with the new wave of CGI shows new cel 
collector's don't surface much.  Simply put there 
is not enough people replacing the ones leaving 
as you said.

"I beleive that in few years, we collectors will 
find that there is nobody out there who wants to 
buy our cels for sale."

   In response, it is a possibility which is why 
I tend to collect and buy cels that give off that 
warm fuzzy feeling.  Thus it becomes more of 
something in personal value vs $ value.  This 
happy feeling getting the cel is priceless (as 
some cc commerical puts it)  But on the other end 
when cels are forgotten and tossed aside (similar 
to the comic books in the past that people just 
threw out) you can help but think that these cels 
may be hot sought out items in the far off future 
after a generation or two.  Don't forget that in 
the future it is possible that all anime will be 
done via CG thus making our current cels even 
more valueable and collectable/rare.  More of a 
memobila/piece of anime history.  Of course that 
is if our cels survives the test of time. LOL.