New South Wales
So if I take the hide action on the card and succeed, I would discard the card to the past.
Yes, as the positive consequence is "Discard this."
At this point, it appears I could take the spot action again from the terrain card and get the other 035 card from the box. That would justify the relatively high cost of the hide action. Am I right in this?
Yes. Discarding the card removes the golden arrow with small action icon as well, making the Spot action on the terrain available again. You could indeed access the other card.
Whether it justifies the cost, I won't say either way.