Okay, setting aside all the other perfectly valid 
reasons for collecting from an unseen series -- 
artistic appreciation, liking a specific designer 
or seiyuu, a wild hare up ones arse, and so on -- 
there's a notable financial element to this issue.

Once a series receives distribution outside of 
Japan, whether it be through TV broadcast or 
video/DVD release, and becomes known to the mass 
market, the cel prices spiral upwards.  We've seen 
it time and again -- it's practically a law of 
physics.  At that point, it really becomes 
difficult for someone to collect all the 
interesting characters or scenes that they might 
have been eyeing before.

"Unknown" shows, however, are generally 
inexpensive in terms of cels.  So if a look 
through the available images tells you that this 
anime may be something that will appeal to 
you, it just makes sense to purchase cels while 
they're still extremely affordable.  Then, once 
the show or movie is finally released overseas, 
you may find yourself with a ready-made collection 
of cels from your new favorite anime.

Or, of course, it might turn out to be a dog and a 
half.  *evil grin*  I guess you could still call 
this a case of cel speculation, but it's 
speculating in personal interest rather than 
monetary value.

One way or the other, I'm very happy with my 
collections of B'T X, Cyber Team in 
Akihabara, and Steam Detectives cels, 
even though I've never seen the shows.  And that 
entire binder put together cost less than my one 
most expensive Slayers cel.

I call this a good thing.

(Cel below - a heart-felt and legitimate response 
to anyone who tells me I can't have it because I 
haven't seen City Hunter.  ^_~)