I can't dispute any of the gloom-and-doom predictions above. There's no arguing about the fundamental facts that have been pointed out already in this thread: the hobby has almost completely lost its popularity among kids, the prices are going up to the point where even the adult enthusiasts have trouble affording them, and the public outside that small community of enthusiasts thinks the hobby is ridiculous (if said public knows the hobby exists at all). In a desperate effort to find something positive to say about the whole thing, though, I can offer the following.
I've read several books about the subject, and (though the thought depresses me in the extreme) I've witnessed almost the entire history of plastic modeling myself. (I built my first one, a Revell DC-7, in 1956 at age 5.)
The hobby of scale plastic modeling was, to all intents and purposes, born in the early 1950s. (There were a few plastic kits, and a few built-up plastic models, before then, but the kit craze really started in about 1953 or 1954.) It took a few years to build up steam, but by 1957 or 1958 scale plastic modeling had become the number one hobby of American boys. (So says Dr. Thomas Graham, in his book on the history of Revell - and he offers plenty of evidence to back up the claim.) The hobby/industry retained that stature through the 1960s, with the number of kits getting bigger, and their quality getting better (generally speaking), every year.
Then came what Dr. Graham calls "the troubled seventies." He offers several explanations for why the popularity of the hobby tapered off during that decade: the rising price of oil, general economic malaise, the decline of patriotism and respect for the military during the Vietnam War, the appearance of the first computer games, etc., etc. (Dr. Graham politely refrains from mentioning another factor that, to my recollection, was also important: a series of spectacularly bad marketing decisions by a new generation of people who were now running the model companies.) Several manufacturers (most famously Renwall and Aurora) went under. Monogram was taken over by Mattel, and for several years didn't produce any serious scale models. The British manufacturers were having similar problems. (Frog gave up, leaving the British field almost entirely to Airfix - which was starting to have serious problems of its own.) Apart from the newcomers on the other side of the Pacific, it looked like scale plastic modeling was sliding down a slippery slope toward total extinction. By the late seventies, the trade journals and the IPMS were asserting that the day of the scale plastic kit was just about over.
Fast-forward thirty-five years and what do we see? The hobby of scale modeling is in the midst of what I firmly believe will come to be regarded in future decades as a "golden age." The number of kits in every field (except the one I happen to like best: sailing ships) is expanding significantly every year. The resin ship kit field has blossomed in the past few years; the number of resin warships on the market is now well over a thousand. The current range of aftermarket parts, in metal and resin, would have been unbelievable as recent as fifteen years ago. (Most of us can remember when knowledgeable authors and modelers accepted that reproducing a radar screen on 1/700 scale was simply impossible.)
There are even positive signs in the sailing ship world, if one knows where to look for them. Model Shipways, Bluejacket, and Calder/Jotika are producing fine, new, scale sailing ship kits - though they take their time. Some, at least, of the HECEPOB companies seem to be waking up and discovering what a scale ship model looks like. The number of excellent books on the subject of ship modeling has never been higher.
As a Certified Curmudgeon I'm convinced that the hobby as we know it is indeed going to undergo some big changes - not all of them for the better - during the next decade or so. I share the often-expressed concern over the lack of young people getting into it. (I'm a member of a fine model club that has about thirty regular members. I, at age 59, am one of the half-dozen youngest.) I have no doubt that, thirty years from now, the hobby/industry will look significantly different than it does now. But my own observations of what's happened to it within my own lifetime lead me to believe that, one way or another, it will still be around.