"What about other areas and under-the-covers code that just
needs rework? Just do what I do, and work on it on your own
time."
Yeah because doing unpaid work for your company is the way to go.Get a life and learn to leave work at work.
It's not the developer's fault if the manager is not dedicating enough man-hours to finish something, only to find out later on that messy code eats up many more man-hours than having it written cleanly the first time with much lower maintenance costs later on.
If developers don't man up and let the managers crash and fail for it, they will be supporting greed and exploitation in the workplace and probably make it worse.