The Stack Exchange software and policies like this were originally developed for Stack Overflow, which is a very large site that needs policies like this to protect the users from spending too much time on things that don't help the site. Here on Japanese.SE, we have a much smaller site, and the burden of a "trivial" edit here or there is close to zero.
I think trivial edits would only become a problem if someone suggests a very large number of edits that don't really help anything. If something like that happens, we can always deal with it then by rejecting the edits. Otherwise, I think we should welcome little edits here and there, as long as they make the site a better place.
Just about everyone on this site is working with a language they're not native in, either English or Japanese, or even both. Fixing typos and such might seem like it doesn't matter much, but it can make things easier for people to understand, even if it seems clear to you without the edit, and so I would almost never reject an edit that fixed a spelling or grammatical mistake (unless there was something else wrong with the edit). I think even small edits like that are good and help the site.
As for your own edits, you might consider looking at the post you're editing and seeing if there's anything else that needs fixing – formatting, spelling, typos, tags, anything. If everything else looks good, I'd go ahead and make the edit anyway. Just use your own judgment, and I think it'll be okay.