I stand corrected, I used "speculative" in two different senses.  Of course all store of value and all monetary assets are speculative in the sense "counting on the fact that someone will put some value for it later".

But what I meant with speculative here is "counting that others will put MUCH MUCH more value for it later than I have to do now".  (to the moon...)

I would say that that is the case for bitcoin for the moment.  People buying coins speculate on a MUCH higher value for them later ("too the moon").  Me too.  

If you would know that bitcoin will have a steady value of, say, $700 10 years from now, I'm not sure you would buy any coins now.

Nevertheless, that's more or less what you do when you buy gold or when you buy real estate as "store of value".  

A good store of value compensates for fiat inflation, and follows economic growth.  
An investment does some more (shares in a company will generate also dividend in most cases).  It can generate cash flow.

I would think that not many people buying gold think it will "go to the moon".  They may hope that they buy low, and that it  will rise, but there's no realistic expectation of a real surge in buying power of gold of a factor of 100 or so.  Which is what bitcoin holders are hoping for.  That's what I meant with "speculative".