As I understand, the reasons for discouraging too minor edits are that they can swamp the review queue, and block the post from actual improvement edits. Still, I often see edits that just change "i'm" to "I'm", which I reject.
But the thing is that the damage is already done: it is taking space in the queue and blocking the edits; and it is certainly improving the post (even thought very slightly). So, I suggest a new rejection reason: Too minor, but valid.
These changes are simple to spot, so only two reviewers should be enough, so we get them out of the way quickly. They do improve the post, so they will be applied; but to not encourage the behaviour, the editor will not get the reputation and it will count as a rejected edit.