Back in the old days, before most of the current puppies were around, we used to have SpinRite to reform the tracks on the drive without removing the data. It picked up each cluster, re-wrote the format markers and centered the track on the heads, and then put the bits back down.
It was considered magic, even by knowledgeable people who had some notion of how it worked (or at least thought we had a notion).
The author is still around, but these days he appears to spend most of his time fighting the hackers and spammers and other criminals.
Defrag will help some, but if you watch the monitor you'll eventually notice that some of the most critical files1 are tagged as "unmovable," and a defrag can't do anything to "refresh" them.
1 No one seems to want to explain what makes a file "unmovable," and they may just be the files that have to be open for defrag to run(?). They do seem to be the same ones every time you run a defrag.