Many people make the mistake to consider cryptos as an investment. 
An investment is a vehicle that gives a direct return in the form of interests or dividends. Since cryptos do not provide that, it is not correct to speak of an investment. 
For cryptos an increase of value only comes into life when people are willing to pay more for it than others. This is called speculation and speculation goes hand in hand with bubbles.  

So I believe that yes we are in a  speculative bubble but not all bubbles have to explode. If the demand for cryptos is great because they are usefull then it is an organic growth. If people buy cryptos but have no idea about them and just buy them to get rich quickly, then it's an unhealthy bubble that will sooner or later burst.  Since cryptos are a bit of boths, I think that we will have an organic increase of value and bursting bubbles at the same time. 
For us as investors or speculators, the important thing is to believe in the asset and to understand it. It is the long term that matters. 

For me cryptos are an amazing tool and an interesting technology. However, I've never bought any cryptos. I just got some from faucets and clound mining. At the time it was worth very little but now...