Ok, so by "relevant" you meant when we're close enough that prices are starting to be meaningfully impacted. That makes sense, but we also won't know when we get there or if we're there already.

It does seem like you're thinking about it in absolute terms, rather than on the margin. The marginal cost of returning gold to Earth will be a function of the rate of extraction: i.e. more rapid extraction will cost more per ounce. So, if there's any amount that can be mined profitably, then prices will fall to the point where terrestrial demand is expected to meet extraterrestrial supply. (There are a bunch of omitted caveats and addendums in that account, but it's roughly how I'm thinking about it.)

Presumably, this is already factoring into some speculators' decisions and it's definitely factoring into the actions of the private space exploration sector.

It shouldn't matter if it is currently economically feasible. What matters is if people believe that it will be economically feasible in the not too distant future.

Let's say you're planning to start a gold mining operation on Earth and it's somewhere super remote. It's going to take more than a decade to break ground and there will be enormous fixed costs. At prices derived from expected terrestrial gold production, this mine can be profitable over the course of 50 years of operation. Whether or not investment is made in this sort of project may well depend on expectations about asteroid mining.

If projects like that are already being foregone, then we are living in a world where resource allocation is based on future space mining output and we're wealthier because of what those productive resources were used for instead.