If there's THAT much stuff and the goal is to only get one thing, why even bother with the rest of the stuff? Alternatively, if there's that much stuff, why restrict it to one prize?

I'd say that, at absolute bare minimum, of the many things you could possibly obtain in the side-quest, aside from the main prize, you can only take three of the things you found back to the main game. They could be ANYTHING-no limits aside from there only being three-but only three.