That idea of value was nice, in the 19th century. While one can come up with a concept of value, that value is not the same for all actors: Value is not really cost of production, but utility. And we also have to consider marginal value: Water is extremely valuable, but we have so much, the marginal value of producing another glass of drinking water is pretty low.
Many things will never be sold for how much they cost to make, because their actual value, their utility, is far lower than the cost of production. And since values and costs of production change over time, it's not difficult to find items for sale for less than the cost of production.
Then we have stocks and bubbles. The price of a stock doesn't just reflect how much it's worth now, but how much it's expected to be worth in the future. This does cover speculation too: There is a utility in holding something if you expect to be able to resell it for more tomorrow. So I'd not say that what people call bubbles has that much to do with being far from fundamentals, but with information being propagated that shows that the current estimate of future value is very different from the current price. If a pharma company is on trials to cure a major kind of cancer, its stock will go up. If the trials are unsuccessful, it might go all the way to zero. But that doesn't mean that there was a bubble. This is especially true with stocks, where, if you really think a price is way too high, a hedge fund can make money shorting it.
So, when calling something a bubble, we have to have some very strong reasons to do so. You could claim that the Efficient Market Hypothesis doesn't hold, even at the weakest of levels, at which point you are very, very far from mainstream economics. You can instead claim that the problem is that the market is being manipulated, and that might be the case with Bitcoin, for instance. Maybe a company is committing major fraud, and most people don't know about it, but you do have insider knowledge. That'd not be much of a bubble, just plain decepcion. You could also claim that there are major amounts of risk baked into the price, so you can expect volatility. Many would argue that the financial crisis, for instance, was really all about the Fed just not making any sense, and not reacting to a sudden increase to the demand of money.
So when it comes to bitcoin, how do you explain the bubble? My favorite is a combination of price manipulation from actors that control way too much bitcoin for a market to be all that efficient, tied to a high amount of variance in possible outcomes. If through something strange, Bitcoin actually happened to become important, then its current price is very low compared to what it should be. If it is not, then the current price is way too high. So what we see is a market that is mostly known by people who are just spending a few dollars hoping to make millions, so for them, it's a lottery ticket. Buying a lottery ticket, hand having it lose, doesn't mean that there was an asset bubble with the tickets, does it? :)