The general strategy is to put all of your low-level goblins to work on any node available until they are ready to be fused with another goblin. That being said, it’s actually better than not having a goblin work on the node since slow progress is still better than no progress. The only downside to a goblin working on a node that is of a higher level is that the amount of time needed to work on that is increased exponentially. However, it is not mandatory for the goblin to have the same level or higher to work on a node for it to start being processed. When clearing out nodes, repairing structures, or opening gates, a specific level goblin is needed to work on them efficiently. Otherwise, you always want to spend your elixirs upgrading your cards that boost other sectors of mining.
Usually, the cards that are marked as uncommon and higher are worth spending Elixirs on. The ones you need to automate are the structures toward the end of the mine.
However, you don’t necessarily need to automate all of your mining structures, especially the ones you see at the start of the mine. The game makes it seem like you need to upgrade all your cards and spend your elixirs at every stage.
