I think it would be kind of interesting to make maps like sigils and Increase the rarity of the reward with the maps spent.
But at the very least, I think the rewards need to be updated. They haven’t changed since the UI upgrade, before Delves were introduced and when Guild Wars was the only guild event.
I recall it was pointed out that a rework of Treasure Hunt mode is being processed.
But no additional info was ever included, so we don’t know how much work has already been done: