I've been collecting for a lot of years now, and I've only ever seen prices move in one direction. I'm sure there's been an acceleration in the rate of increase recently, and I certainly agree that the current prices of loose figures in particular is ridiculous at times (I too was watching the eye-watering £250 Tri Fett on eBay, but I certainly wasn't paying that for it!). I think the point is that Star Wars has always attracted new fans, both to the films and the toys. Even in the early nineties I knew avid vintage collecting kids that weren't even born when Jedi came out. These films and this hobby attracts new fans and always has. And of course there's also then the inevitable nostalgic drive for many of those kids, once they've grown into adults, that makes many of them want to recapture their childhoods, and hence buy the figures they owned previously but sold (to buy a BMX, in my case... and it wasn't even a good one!).
Will the bubble burst? I doubt it, not for a long while yet at any rate. Previous generations had their dolls, train sets, Corgi and Dinky, etc., and whilst they do remain popular, I doubt that popularity will last significantly beyond the generations that owned them as toys when they were children. Star Wars is different and always has been a special case due to the way it attracts new fans. I'm sure Corgi and Dinky attract their own share of new collectors too, but it won't be on anything like the same scale (i.e. percentage numbers) that vintage Star Wars does. And of course, Disney hoovering up at the box office every year from now until the end of time will keep Star Wars in the news and consciousness of current and would-be fans and collectors for years to come. Some fans will doubtless tire of the new films, especially if they're poor, but the original trilogy will always be there, and if anything, the new films being poor may well only serve to remind people how good the originals were and hence push still more collectors our way.
I have often wondered how many kids that owned the modern Hasbro Star Wars toy line will feel nostalgic about it in later life. Many doubtless will, but the prices of the pieces will never compete with vintage due to the sheer difference in the available quantity of each, not to mention the vast difference in the number of different toys available in each of the lines. Vintage collecting therefore has many different reasons behind its enduring popularity, which inevitably mirrors the popularity of the original trilogy. Yes of course The Force Awakens has kindled or rekindled interest for many new collectors (and the inevitable scalpers and investors) to enter the marketplace and drive up prices on vintage items, but a lot of those new collectors will stick with the hobby, like most of the people reading this have doubtless done. So in conclusion, I think sadly, high prices are here to stay for quite a while yet... But of course, I have been known to be wrong... from time to time... or was that R2? ;-)