“Good enough” is defined by the inability of stakeholders to conceive of transitive benefits. Compute performance suffers the tragedy of the commons.
The whole point is that there are absolutely no benefits, at least relevant ones, once the performance is acceptable. It's a diminishing returns game. There is always a tradeoff between performance and cost, and once performance is acceptable then it's hard to justify wasting more resources to get nothing of value in return.
Define acceptable. (Hint: you can't)
Once you are talking about tradeoffs, it's game over. The question is, do you want to have spent your programming career writing crap code? Or do you want to make each thing you do be something you can be proud of, that is better than you would have done last week?
There is always something that could be done to make code faster, or shorter, more parallel, or line up columns better. What matters is whether you are pushing yourself to improve every day. If you improve yourself by discovering ways to make code fast, you will always find new ways to improve, and your improvements will also often make life better for other people.
If the quality of your code has no effect on anybody's life, it is time to find something else to code.