If it ain't broke don't fix it they usually say, but sometimes that simply does not work. Just like a few weeks ago, when I came home and saw the concrete beam above my front door, totally dirty from the moss that had collected on top of it, which colored the rain dripping down from it, staining the front to a color that was many shades darker than the concrete of my neighbors' homes. So I took the pressure washer, and made it shine again.
At work, similar stuff happens: I will see something that needs improving, and always leave the place cleaner than I found it, like a good little boyscout. But of course you need to make sure there is time in the project to do such things. If you end up in a situation where manual testcases are never automated, your test work will suffer and even come to a halt as the burden of keeping the testing updated with the changes in the software grows out of control!