I would like to have the old mining on planets.
I believe the average size of ore-nodes should be bigger, and maybe amount of ore-nodes should be less than one year ago.
However, the feature is great, and, since we have asteroids, why can't we have the same on planets? -- I mean, to have mining with closing tunnels automatically after some time ( the same, how asteroids just get refreshed ).
If player wants to have the cave, - make a game-mechanic that will "mark" the soil modifications to exist for some extra time (+1week, next time +2 weeks, next time + another time..) That is how cave and tunnels can remain active, - by player maintenance), else it will be refreshed automatically.
Best regards,
m0rrty