Actually, the mundane values might have been linked quite a bit. Remember how (rogue) monster spawns appeared widespread during the Invasion, and (rogue) undead spawns became non-existent after a while? Also, recall how certain (rogue) undead spawns were disturbingly powerful even in small numbers, much smaller than any typical undead horde. That suggests to me that the "random" spawn rules got tweaked such that they were no longer governed by something like "At monster/undead value of X, spawn Y monsters/undead".
I have a feeling though, from one of the Prophets, that simply destroying them in battle would not have reduced the value appreciably. This is because I am pretty sure there's not a 1:1 correspondence between the value of the "resource" and the quantity of troops that can be gained from them. I'd guess that especially for undead, the ratio of undead recruited to resource available was very high, such that even if a couple thousand undead were defeated in pitched battle, the actual available resource wouldn't have suffered much of a dent.
And considering that every region has its own values for these things (I'm pretty sure everyone who's played an adventurer knows this by now), that means some places might still have a really high "resource" value.
