To tulips and beanie babies: There were direct substitutes (other flowers and other stuffed animals) in terms of the actual utility, but tulip prices shot up in 1637- even investors bought tulip contracts not because they needed them, but because they were speculating on the value. Eventually demand leveled out, and the prices stopped going up. When the prices stopped going up, the speculators got out, and prices went down fast. The premium status of being the preferred flower or the preferred toy didn't help any more. How could this be like BTC? There are cryptocurrencies that are direct substitutes like LTC, but BTC is preferred and has a lot of investors purely for speculation. Once demand levels off (it must, there are a max of 7 billion people that can buy it), the speculators will get out, and prices will come down. Why hasn't it happened yet? BTC is artificially scarce due to block difficulty increases and fixed BTC being added for each block. The limited supply is maintaining price support for now, but like I said, once demand levels off, the fixed supply won't be as big of a price driver.

Similar to houses and .com stocks: Houses have real utility (you can use it for shelter). Stocks have real utility (you own a piece of a profit making entity). BTC has some real utility (you can transfer wealth outside of the regulation of governments and banks). However, these bubbles happened because instead of trading on a firm foundation value, people started expecting profits. The castle in the sky theory does work, but only if enough people believe in it. Once confidence faltered (either that people would continue to buy houses or that .com stocks would continue to print money), the castles in the sky fell, and prices fell back to their firm foundation value (a house in Las Vegas that I looked at went from $400k down to $100k- basically the price of raw materials and cheap labor). BTC's price right now is WAY over it's firm foundation utility of being a wealth transfer vehicle. It does have some value, but if enough people decide that a couple other cryptocoins can do the job with less risk than BTC, then prices for BTC will go down to it's intrinsic value- mostly related to the price of energy. It's hard to tell where this will settle, because ASICs are getting more efficient, and the block difficulty changes. But I guarantee you it will be way under $6k.

So these things aren't exactly the same, but there are lots of similarities with previous bubbles in the past. I'm not saying to stay away from BTC, but you had better be willing to lose your investment. There are a lot of people in the market that are only looking for a quick buck, and if they get out before you do then you are going to lose most of your investment. If you aren't desperate to make money off your investment, you will be happy with closing a position early instead of riding the crash into the ground. Closing early makes you the person with the quick buck and makes someone else the fool that lost their shirt.