The rejection reason “too minor” was introduced for several reasons:
- Edits bump a post on the home page, giving the thread more attention. This is desirable in case something major has changed, but not to fix a typo.
- Suggested edits cost time for the reviewers.
- Each edit used to bring the post closer to community wiki status — but as you note this is no longer the case.
The third reason no longer applies. The second one does, but only to a small extent: manpower for suggested edit review used to be scarce on Stack Overflow, but now it is no longer, and it never was to my knowledge on any other Stack Exchange site. The first reason still applies, but it isn't a big deal unless a lot of minor edits happen (and it's a big deal even for major edits if there are a lot of them).
There's been much debate lately on Meta Stack Exchange and Meta Stack Overflow, with opinions ranging from generic frustration against suggested edits to wanting to do away with “too minor” altogether. Given the complete lack of consensus, don't expect the reason to disappear or change.
I only use “too minor” in a few cases:
- The suggestion isn't really an improvement, it's only cosmetic. For example, an edit that standardizes a post that mixes British and American spellings (on a site other than ELU or ELL, where that can be important).
- The suggestion corrects a few problems but there are many other glaring problems. For example, an edit that fixes the spelling of one word while leaving many other grammatical mistakes, or an edit that removes an inappropriate tag but doesn't add other tags that the question sorely needs.