Gold fluctuates +/- 20% vs. the dollar in any given year which I would consider quite "wild" and it's used globally as the currency of last resort. And the current demand for gold as a commodity in e.g. semiconductors hardly justify its lofty price. So I'd say gold is just as speculative as bitcoin in that sense, but perhaps less volatile.

The value of bitcoin is predicated on the belief there is a limited supply, just like gold. The difference is that in one case the mechanism for limited supply is the Earth and the other is proof of work (which is more fallible than Earth obviously).

In any case I don't think BTC is meant to be _used_ as a daily transaction medium (just like gold is not), no matter how much BTC bulls would have you believe it should be. But as a long term store of wealth holding BTC is like a riskier version of holding gold, with the same fundamentals driving the price.