It occurs to me that one way Bitcoin might indeed be different from all previous bubbles cases where assets have greatly and rapidly increased in market value out of proportion to any increase in intrinsic value of the asset, is the existence of very large holdings that were initially acquired for almost nothing.
It always cost a nontrivial amount of money to source and transport a tulip bulb. That made it unlikely, if not impossible, for anyone to have been holding stockpiles of thousands or millions of them at the time of the market mania. Similarly, Beanie Babies were never available for a penny, a dime, or even a dollar apiece; therefore, while casual collectors sought variety (e.g. one of each new issue), the "investors" tended to focus on items believed particularly likely to rise in value, such as "rare" discontinued items and "limited-edition" releases, rather than sheer numbers. Neither practice resulted in many Beanie Baby paper millionaires.
With Bitcoins, early investors could buy in much larger numbers than latecomers. If I'd wanted to invest my retirement savings in Bitcoin in early 2011, I'd have bought several hundred thousand of them; at today's price, a few dozen. (Being a stodgy low-risk investor, the growth of my retirement savings through those years only has a small relative impact in that figure.) The recent "shoeshine boy" buyers, all told, can only afford a relative few compared with the early acquirers.
It would be interesting to see the distribution, or even just the mean and median, of acquisition cost (mining cost or purchase price) of all the bitcoins in existence. I suspect the median especially is actually quite low, and that large holders dominate that part of the distribution.
About half of all bitcoins were mined during or before the first quarter of 2012, when the price was in the three to five dollar range. The mining cost was presumably less than that (as mining did not cease). That gives us a starting estimate for the median acquisition cost of all coins currently held. Of course, a high churn rate since then (a large fraction of the bitcoins in existence changing hands since then at higher prices) would raise that median, but if that hasn't been the case, then there's still a large pool, a deep cold ocean so to speak, of Bitcoins that were last acquired at very low prices relative to the current market price. After all, at current prices it doesn't take many Bitcoins to keep the short-term speculators occupied.
So, what might be going through the minds of such large low-acquitision-cost holders? Imagine you own ten thousand Bitcoins that cost you ten thousand dollars to acquire. They're now worth a hundred million on paper. But nobody's buying them in such quantities at current prices. New hundreds of millions of dollars aren't flowing into the market. (They were for a while, but more recently they've been flowing out again, as sellers act to take profit or cut losses.) An investor like you once were, who wants to take the risk and buy in with ten thousand to invest, can only buy 0.01% of your collection. You need 10,000 people like you to replace you in the market, or one person willing to risk 10,000 times more.
You can still make huge gains by selling, but you'll take a big loss in paper worth in paper worth in the process, as your "dumping" lowers the price. On the other hand, you can keep holding, and the price might start soaring again. Or at least, if the market price stays in its current neighborhood, you can maintain a steady stream of income by selling a few at a time.
You can help keep your asset healthy by doing a little additional speculation of your own, buying the dips and selling the peaks, making enough profit along the way to offset the additional risk you're taking. Your own transactions won't make much difference, but if much larger holders also do the same thing, for the same reasons, that will support a floor on the market price, at least for a while. One drawback is, the one asset you can't use to fund this practice is your Bitcoin worth itself, so the support of Bitcoin-millionaires and Bitcoin-billionaires is dicey and might not be sustainable long-term.
If there's a "deep cold ocean," it needs to stay quiescent instead of churning up and cooling the market. That's quite possible, while those holders remain satisfied with paper wealth and future prospects. But every time one decides buying a better home or paying their kid's college tuition or traveling abroad while they're still young or paying medical bills or investing in some newer hotter thing has become a higher priority, the applecart would come a little closer to upsetting.