What happened? To start, the book was printed in enormous quantities. After the first few weeks of sales, when new shipments of the issue arrived in comic stores, the book's price began to drop. The long-term value of the book was also adversely affected in two ways. First, Superman returned to the comic scene, alive and well, a mere four months later. This may have been a surprise (or an outrage) to many of the non-collectors who purchased the book, but was not much of a shock to the average fifteen-year old Superman fan, well acquainted with the 'dead today, back tomorrow' mentality of the genre. Finally, the black package or "polybag," while supposedly designed to preserve the book, was actually made of a cheap, slightly-acidic plastic that would eventually turn the issue's once-white pages to a plaque-like brown. Thus, collectors were forces to decide between damaging their copy of Superman #375 by opening it or by keeping it in it's corrosive wrapping. Both paths ultimately led to a drop in the book's value.
Sadly enough, this sort of hype with no follow-through occurs on a near-monthly basis in the world of comics. Major publishing houses routinely emphasize the 'collectibility' of their output, hoping to snag the attention of young collectors eager to validate their hobby by earning a bit of cash on the side. The simple truth is that the vast majority of the comics that are produced today are highly unlikely to become valuable, mostly because of one simple, undeniable fact.
Today's comics are published in enormous quantities. A typical issue of The Amazing Spider Man will have a print run between 300,000 and 500,000 copies. With that many copies of an issue available in the marketplace, a savvy collector will never pay more than the issue's cover price: she or he will just keep looking until they find a copy still on the shelf. Furthermore, Comic book stores often stockpile crates of 'collectible' issues in their store rooms, flooding the market with their overstock the second that the book rises in value. X-Men #1, the first issue of a new X-Men spin-off series published in the late 80's, had a print run of 5,000,000 copies. Today, despite speculator hopes, the book is often sold for less than its cover price.
The comics of decades past were treated like newsprint. Children purchased books that are worth thousands of dollars in today's market for a few pennies. They read them, they enjoyed them and, finally, they discarded them. Modern day collectors are astounded and appalled when they find potentially valuable books in their grandparent's attics 'defaced' by childish doodling or crumpled and forced into remote, dusty corners. This paradigm shift has completely ruled out the possibility of any 90's collector owning the next million-dollar book: comics are now recognized as a collectible commodity.
Today, the comic book marketplace is an institution geared towards perpetuating the illusion of collectibility, a world where everyone who purchases a book is a collector. Even the youngest child knows not to damage his or her comics. After all, they might send you to college one day.
The sad truth is that items become collectible when they are overlooked. With nobody overlooking comics, how can anyone honestly think that they are sitting on a gold mine waiting to happen? If you're sitting on it, chances are that there are fifteen other people on your own block in the same position, with the same books and with the same unrealistic, hype-fed hopes and expectations. If you've already purchased a lot of books, don't be disheartened. Your investment will likely prove to be a monetary failure, but you're probably sitting on a wealth of high quality storytelling and illustration. If you haven't yet cracked open that copy of Superman #375, do so. Despite diminished collectibility, comics can still be very good reading.