Was anyone talking about.com bubble blowing up before it actually did ? Speculation of crypto bubble blowing up may actually be built into the cost
There was common discussion about junk dotcoms like TheGlobe.com, DrKoop.com, Geocities and dozens of others, and how they had no actual sustainable business (and often no plan for when they'd develop one). Scient, Viant, Razorfish, MarchFirst, and dozens of dotcom service companies were granted crazy valuations versus existing traditional peers (which is history rhyming re Ripple vs PayPal/Stripe/Square/Ant/etc).
The high burn rates, the lack of business models to actually make money, some that went public with practically no plans for how they'd make money at all, extremely high valuations on the few that were making money, and so on. These things were all very widely discussed, many skeptics were shouting about it, it wasn't popular to give them TV talking time (channels/sites like CNBC et al have a vested interest in pushing exuberence).
Because of that, I don't think the possibility of the bubble popping can be built into the cost in the way you're implying. If you think there's a 20% chance your investment will dectuple and a 80% chance you'll be wiped out, you can split the difference to find your expected value. But since none of the market participants believe the current value is the long-term value, eventually it has to land one way or the other.
Admittedly, the speculation that crypto currencies are a bubble does seem even stronger, but personally I don't find that surprising: it did seem feasible that .com companies could coexist, whereas crypto currencies seem to be offering the same product.