No all abbreviations are bad, a lot depends on context. In simple cases, when they are perfectly understandable, abbreviations should be fine.
Even if some existing code should benefit from expansion, it may be better to just leave it alone and wait for some substantial reason that requires touching that code, and then improve on style if necessary. Someone needs to review these PRs, and pure coding style improvements (which are often in the eye of the beholder) may not be an efficient use of their time.
Also, if there are no explicit violations of a specific coding style, it may be fine to assume that the person who wrote some code and got it accepted as a PR is an experienced programmer who knew what he/she was doing. You may do some things differently, but that alone might not be a good reason for a PR.
Finally, I think it is great if you have time for contributing to Base and the standard libraries with an eye to small details. There are many minor open issues that could benefit from your work.