I don't see the problem with accepting edits that are 'too minor' in one person's opinion. It's been discussed dozens of times on the main meta.so site, and the outcome is always the same:
Minor edits to questions that improve grammar, readability, capitalisation, code formatting, remove salutations etc, are all perfectly acceptable, and indeed encouraged, as long as the golden rule is upheld - if you're going to edit a question/answer, make sure you fix everything that is wrong with it.
If all that's wrong with a question is some minor grammar/spelling issues and/or a salutation, then fixing only that is perfectly appropriate, in fact it's the mandated thing to do.
if the meaning of the question is clear, I think it should be strictly left alone
I'm afraid that's not how it works on the Stack Exchange network - these are collaboratively edited sites and any question/answer is fair game for editing for any number of reasons. For example - if the meaning of a question is perfectly clear, but someone wants to go through and capitalise all the I's that an OP has missed, then that edit should be accepted as it improves the quality of the post.
Just because a question/answer is clear/comprehensible, doesn't mean it's perfect, and that it can't be improved upon.
the Queen's English format hides the fact that the OP is struggling to express himself in a difficult language
It may sound harsh, but that's not an issue we need to worry about. Remember, we're creating a repository of questions and answers for the future; the fact that the OP is struggling in a certain language is completely incidental to the quality of the question, and totally ephemeral information.
Think 2 years down the line when someone stumbles across the question/answer. How could knowing the OP doesn't speak English properly help them at all? It couldn't. Conversely, the fact that the post had been edited into shape, into proper, grammatically correct English, will actually help that person to parse the information more quickly and easily. And that means we've done our job properly.
Correcting their grammar and making the question properly readable by speakers of the English language (this network's stated audience) is actually a service we provide. For free :)
At the end of the day, what harm can be done by making sure every post is grammatically correct? I would argue that there's none at all.
There's also another way of looking at it - you are a trusted member of the community who has earned the privilege of reviewing edits through hard work and service to the site. I'm all for guidelines, they definitely help, but opinion will be fragmented here so it might not help.
I think it's fair to say that whatever instinctive judgment you make about an edit will be a good one. If a pattern of strange edits was to emerge from your account we'd probably engage with you about it, but I doubt very much that would happen.