I find it very anticlimactic that we can find a cave and start mining as soon as the game starts. I enjoyed the struggle of finding metal and building a mine.
It would be nice if cave walls could only be mined by pickaxe. That way you would have to make a mine hole to get metal. If mines cost too much early game, they should have their price reduced when built on the overworld.
Having content gated by requiring to do other stuff first gives players something to look forward to. Once you get a pick, you can start cave prospecting, but before that you have to use a mine (or just trade).
A minor additional note, if cave walls can only be broken by pickaxe, can we make it so they never cause cave-ins?