But "given perfect knowledge of all market prices and individual preferences at every time and place, as well as unlimited computing power", you could predict how people would choose if they were not faced with legal and moving-cost barriers - e.g. imagine a philanthropist willing to pay the moving costs. So your objection to this metric seems to be a surmountable one, in principle, assuming perfect knowledge etc. The main remaining barrier to migration may be sentimental attachment - but given perfect knowledge etc. one could predict how the choices would change without that remaining barrier.

Applying this metric to Europa versus Earth, presumably Europans would choose to stay on Europa and humans would choose to stay on Earth even with legal, moving-cost, and sentimental barriers removed, indeed both would pay a great deal to avoid being moved.

In contrast to Europans versus humans, humans-of-one-epoch are not very different from humans-of-another-epoch.