The only way to calculate the value of Bitcoin is by supply+demand - like for the vast majority of other commodities. In this moment the demand driven by the hope for the price to be higher exceeds by a lot the demand of Bitcoin for other uses (including investment, Darknet purchase, international transfers of value, etc.).
sorry but how hope for price to be higher is different than investment? and yet you those two are putting in opposite camps? people are buying bitcoin treating it as investment and because others are closing its investment the price goes lower so how is that a bubble? to me its normal behaviour of unregulated stock and not a bubble.
Investors are less akin to undertake a big risk, so they ideally buy when the price is stable and plan to hold for X years until a certain goal is reached. I will give you a practical example: I invested in Bitcoin when it was at around $13, which was a price that held for a long time. Now there are no investors looking to spend money on Bitcoin, at least no "serious" investors, because they know the price is currently overvalued. As soon as Bitcoin becomes again a good investment (<$50) more money is expected to be thrown at Bitcoin.
Speculators are more gamblers, they are into high-risk, quick-profit trades, and if the gamble go wrong, they just close their position ASAP - wash, rinse and repeat.
And what investors will do if price will never be lower than $50 because there is less bitcoins produced for example and more people wants them and those who are holding large amounts are rich already and don't need to sell their big stacks of bitcoins any time soon. Isn't it a gambling also? I don't see a difference. All i know is that you sold your coins, convinced your friends to do the same and now hoping the price will be lower so you are convincing everybody else to sell so you can buy cheaper. The problem is they might not believe you and do the opposite like they are doing now.