Whether one should invest in bitcoin or not depends on whether you think Bitcoin will become a long-term trusted store of value.
If it does become a long-term trusted store of value, BTC should trade around $2,000,000 a coin (depending on how many coins are lost and are actually in circulation). That is over 100x the price of where BTC is today.
If BTC does not become a long-term trusted store of value, its likely price will be close to zero (unless it becomes a "cool" collectible... which is a possibility).
So if you think BTC has a 10% chance of becoming a long-term trusted store of value, it is a good investment with a nice expected return. It is still very risky but professional investors should invest some small portion of their portfolio in this case.
Well its hard to tell if bitcoin is trusted for a long-term investment but I do believe that it is capable because if you were in this world before perhaps you have been seen the long existence of Bitcoin and what it is capabilities. In fact, if you had invested in the year 2009 I am pretty sure that you are now one of the successful people. Regarding the question, if bitcoin will be a long-term investment, my answer is definitely yes.