The amount of candle/battery usage per use of mine is really high and makes upgrading the mine impractical. Yes, as Hydromancerx mentioned in a previous post it produces higher tier loot that the previous mine could not, but this makes mining for the lower tier loot unfeasible as you consume more resources to get the same amount of lower tier loot. Honestly it is more viable to cross your fingers and hope for another augur so you can build a new mine hole then mine for the lower tier loot in the dark mines. That's why I think that dark mines should be buffed in a sense that the lower tier loot, when harvested from the mine should come in larger quantities. The quantity you get should depend on rarity of the loot, as you'd often find lots of stones, bones etc but you would find very little sulfur. For example, if you harvested iron ore from the dark mine you would get 7-8 ore per use, or if you harvested stone you would get larger quantities (since it's more common) like 15-20 of them per use. Another way to buff the mine is to make the battery and candle usage decrease the further you upgrade the dark mine. Honestly, when I imagine upgrading from a dark mine to a dark mine with pulley then to a dark mine with a steam pulley, I imagine the character being able to move faster as he's able to move the ore more easily. Thus, it seems realistic that the character would use up less of the candle/battery per use. These are a few ways that can make the dark mine feel more like a true upgrade then just a downgrade.