I think if the cost per elevator was changed to 12, and the party all contributed towards that 12 instead of each paying, it could reduce the CE strain on us while promoting group runs and things would still be balanced. If it's set at 12 that's 3 CE per person in a 4 person group. 4CE/per for a 3 person, 6CE for a duo, and 12CE for a solo.
Just a thought.
I'm not in favor of increasing the energy for a single player run. Because stuff can happen and you can suddenly find yourself alone out of nowhere (people having to go, disconnections, and so on).
Say you're on a run as a duo. You have 10 energy left. You and your friend reach the end, well the friend decides to leave. Then you're SOL if you don't have CE.
So even though it won't create an even divisible by 3 method, I say go with everything you suggested but if you're alone, it maxes out at 10.
And with that said, I'm going to leave before others show up saying that this would make the game too easy or that it would ruin any incentive to play on future reduced energy weekends, and so on.