People can do whatever they want. 

Personally, I just think that speculation hurts 
the market in the long run. There was an 
interesting chapter on it in Extraordinary 
Popular Delusions and the Madness of Crowds by 
Charles Mackay. He talked about how the tulip 
market went mad in Amsterdam, people paying their 
entire life savings for a tulip bulb in hopes 
that someone else will buy it from them at a 
higher price. It worked for a while, but the last 
person to buy it got screwed. No one was going to 
buy their tulips and they lost a lot of money on 
them. The same thing happened to the card market 
and the comic market, especially on the things 
like number one issues by "hot" artists and 
Chroma and laser printed covers. Hey, Neil Gaimen 
agrees with me. 
Nothing anyone collects will make them a 
millionaire or pay for their way through college. 
Not unless you're willing to hold them for fifty 
or more years. . . .  Well, Beanie Babies, but I 
think the market's coming down on them. 

I'm NOT saying this will happen to cels, because 
it's not like they're made in huge quantities. 

As a collector a good rule of thumb is to buy the 
things you love. If they go up, great. If they go 
down, too bad. At least you'll have a reason to 
keep them. :)You'll also save money from the 
things you bought that you thought would make you 
a millionaire. 
Hey, Excalibur issues were $10 at one point, but 
I still like them, even though they're only worth 
a quatre now.