It's a fascinating and important question and it's definitely right to be asking it.
I always think that most CE collectors will have fallen into it after a history of gaming from a relatively young age. It will have a very strong personal element which will quite possibly stay with them most of their lives. In that sense, it is less likely to be a short-term fad or trend for a given individual.
Others might start for other reasons - they are habitual "collectors" and gaming is something that interested them and seemed relatively collectable. Quite often that type can become quite involved in re-selling or collecting only sealed editions etc.
The latter can also tend to focus too much on the "value" of their collection, the relative rareness of their collectibles versus others and on the extrinsic value placed by others on what they have collected. That type of collectors is going to be more vulnerable to shifts in societal attitudes and may find their interest wavers as the next big things come along.
Ultimately, I think if you are collecting for the "right" personal reasons then the external environment, societal trends, fads and fashions are all totally irrelevant. I'm not going to enjoy my collection less because it's no longer well catered to or particularly relevant to current industry trends. It's something just for me - I have always gamed and loved the paraphernalia that surrounds it. I open everything I buy, never buy to re-sell, display everything and never, ever worry about "completing" sets. I only buy what I want, if I really want it and if it's at a price I can afford.
I guess what I am saying is judge the value of something by what it means to you, personally, and whether it makes you happy, not by any extrinsic measure. If you do that, it can never be a fad!
Also, I wish I had kept my pogs
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