The fundamental value of the bitcoin system is the value of all the trades enabled by it (minus all the electricity burned). Unfortunately this is hard to estimate - because of two things: we don't know which part of a bitcoin transaction goes to the new owner and which is just the rest going back to the original one, and we don't know which of the transactions are truly non-zero-sum trades and which ones are just speculations. My intuition is that 99% is speculation (and the rest is mostly drugs).
Once we establish the value of the whole system - we can divide it by the number of bitcoins in circulation and get the fundamental value of BTC.
bitcoins, IMO, has value beyond its means-of-exchange, store of value property.
Bitcoin's value is also in the elimination (or reduction at the very least) of trust in financial institutions, governments, counter-parties, third parties, auditors, or regulators.