I always took it as "leave it better than you found it" across the files that I've been working on (with some freedom as long I'm on schedule). My focus is to address the ticket I'm working on. Larger improvements and refactorings get ticketed separately (and yes, we do allocate time for them). In other words, I don't think it's misguided.
I do not believe in "boyscouting". I think if you want to leave it better, make a ticket and do it later. Tacking it on to your already planned work is outside the scope of your original intent. This will impact your team's ability to understand and review your changes. Your codebase is unlikely to be optimized for your whimsy. Worse though is when a reviewer suggests boyscouting.
I've seen too many needless errors after someone happened to "fix a tiny little thing" and then fail to deliver their original task and further distract others trying to resolve the mistake. I believe clear intention and communication are paramount. If I want to make something better, I prefer to file a ticket and do it with intention.
Boyscouting works because you don’t need to get permission to fix tech debt when it is bundled with something else. 98% of those tickets you file to fix warts will never be addressed because the business demands that time is spent on features that make money.