Ultimately, the matter of how to net the most coins in the long run is what needs to be settled in my mind, and as a result two questions need answers in my mind right now: is it possible to stay below both the Oil soft cap and the Coins soft cap? And if not, then which is less damaging to waste: Coins or Oil?
To provide some context: outside of events, I exclusively use Oil on 12-4 (a negligible amount goes to META Showdown, but I will ignore that for now). So we're going by 12-4's Oil to Coins ratio, which I have computed to be 350 Oil to 2k coins, roughly.
Over the span of 36 hours, one can have both the refinery and the merchant go from zero to the maximum amount, which is 3.6k Oil and, respectively, 12k coins. 3.6k Oil, provided one only does 12-4, can be used to farm roughly 20k coins, which is more than what the merchant would provide. Based on that, I am asserting that the Refinery's returns are more valuable than those of the Merchant's. Which means, if I had to choose which resource to let overcap of the two, it would be coins.
But that assumes it's even necessary for one to overcap. What way would there be, then, for neither of those to overcap? To really stay below the Coins soft cap, you'd have to not do 12-4, which in turn causes Oil to accumulate, running the risk of it overcapping. But to do 12-4 and use that Oil is to have coins eventually overcap. There is one way to stay below both soft caps, and that is to spend more, but that's not preferable to me and I would avoid that if possible.
To those who are willing to think about this with me, I am sorry for this wall of text. If you made it this far, I would be happy to hear your thoughts.

