This game is absolutely fantastic. I was searching to replay Motherload when I came across a far superior version in this. I will anxiously await a sequel to this (underwater searching perhaps).
Combining my opinion with the comments below here are a few suggestions:
1) Ability to visit a previous planet or fixed planets instead of random travelling.
2) More upgrades but less clicking, if you have the inventory to build the subparts that should be done automatically somehow, although this might be very difficult for you to code.
3) Maybe have a system where you must gather enough fuel or resources before your ship can leave a planet.
4) C4 or bigger explosives than dynamite (like Motherload has)
5) Ability to drill into full lava pockets to collect a large glob but resulting in massive damage.
6) Maybe enemies or a boss of some kind but try not to do it like Motherload, I really didn't care for the C4 spamming boss fight.
Congratulations and this game should have been way higher than daily 3rd place, its pure excellence.