Most helpful skills?

[Kazeto]

Oh well, happens.

And that being said, Shuttle Ace gets less seemingly overpowered once you get far enough, as by that point you'll have a high enough oxygen limit that exploring the whole planets will not be a problem even without it. In fact, I forwent the skill completely during my last run and I didn't really regret it; it's useful, I admit, but not a must-have sort of thing.