I'm by no means an expert on the topic, and I don't have any specific examples to cite, but it seems like an almost weekly occurrence to read about some cool new technology that will 'never' be economically viable, due to the cost of the 'unobtanium' required to mass produce it (holy long sentence batman...).
It seems likely that the end result of a massive influx of rare materials would simply make 'never' happen a whole lot sooner. While the price would obviously fall (likely by quite a significant amount, that's kinda the point), I doubt it would fall to the point of being 'worthless.'
So then this is basically a bet on being able to "make 'never' happen a whole lot sooner". Or maybe they have someone in the background saying "sure, we can build the antigravity device / FTL drive but we'll need an mega-ton of platinum to make it work". The other alternative is that they believe all the "future of mankind" stuff...
It seems likely that the end result of a massive influx of rare materials would simply make 'never' happen a whole lot sooner. While the price would obviously fall (likely by quite a significant amount, that's kinda the point), I doubt it would fall to the point of being 'worthless.'