Really if you want to invest it comes down to whether or not you think bitcoin will be used as a currency in the future.

Currently what keeps bitcoin afloat is the criminal underworld using it widespreadly over the darknet and Japan itself having somewhat adopted it.

That causes bitcoin to continuelly be used as a currency.

What will cause bitcoin to go up in value is if more people continue to use it.

Personally I believe the people currently using it will continue to use it and more people will use it as we progress and the word spreads.
This is why It is still worth investing.
However currently with the amount of people using it as a currency its current value is fairly accurate.