Like most people of our generation, I began gaming with Airfix, only later graduating on to metals when I started work. If the influx of plastics weans people into new periods or as an alternative to GW, then that has been a success. The market, as it stands, seems to be staying with the old faithfuls of wargaming and is even duplicating itself (British/French Napoleonic and Vikings, for instance). They may well saturate themselves out of a market. We have also seen the rise and fall of prepaints over the last few years. As you say, time will tell.
As for Minifigs, figure quality has moved on a long way since they were fashionable, Perry metal figures, for instance, are about the same price, but differ greatly in appearance