So, we use oxygen as a "food" equivalent. I like it, as it is. Hunger is redundant.
If O2 wasn't unlimited you'd have to make organic farms (o2 production and collection), build a chemlab producing it (water electrolysis - either from collected ice or pipes connected to river/sea) or construct a condenser (if specific planet's atmosphere contains oxygen). For me - sounds like fun. But this game is casual, so..
To keep it as it is, we should make sure that player won't die because of lack of oxygen - base and vehicles with basic o2 supply. So, yeah ulimited oxygen - you could say - nothing has changed. But..
If we could make another use of O2, then things mentioned in point 1. would become profitable. You could build o2 tanks to keep it's excess and then use it to:
burn fuel (shuttles/thrusters/maybe fuel-powered generators)
produce metal alloys
make explosives (mining)