Here's a thought/question: You talk about reclaiming ruins and beasties guarding ancient hoards and so on. If, as an adventurer, you come across a map to a famous place, it would make sense for that place to already be picked over, or taken over, or somehow devalued. On the other hand, if for example you find an esoteric map in some forgotten ruin, chances would be higher that the ruins lay untouched. Do you have any plans to move past the guardian beast as a catch all for ruins, perhaps using it instead as one of a number of situations in which you might find ruins?
This brings up the question of sellable/exportable maps. In dwarf mode, if maps are a top export of your fortress, perhaps you would draw more (and more skillful) immigrants, maybe even drawing from dwarven civilizations other than your own, along with a higher risk of invasion, or looting, or whatever. Fame has its benefits and its costs.