There is nothing wrong with asking for an explanation for a down vote. Particularly if the post is showing a negative vote count. If you made a post and it's not obvious to you why it is getting down voted, asking is the only way you will get a clue. Assuming that the down voter(s) did not leave a comment.
Even if the person who down voted does not indicate why, one of the core community members who is choosing not to up vote can probably explain what the issue might be. (i.e. "I am not the down voter but I consider this..")
A casual down vote that, leaves the post with a net up vote is probably not worth addressing. As an example I have a question on a sister site where I know very little. Currently it is showing 27 up votes, and I have gained 138 rep from the question. I don't have enough rep to see what the actual vote tally is, but I know it has collected some down votes. It really doesn't matter what the few detractors think. There is no reason to modify the question. Over all the community finds value as written.
There is no reason to edit the post just for the sake of editing. If you ask for an explanation of a down vote, and responses causes you to edit the post, then so be it. If not it is highly unlikely the someone will come back and change their previous vote.
What will happen with a small pointless edit, is that the question will circle back to the top of the question queue (new edit). The core community who did not up vote your post last time will get it brought to their attention again.
Personally if I see a poor post, get edited without a net improvement I am more likely to down vote it the second time. In my case that probably means I will leave a comment as to why as I try to usually leave a comment with a down vote... But in general I think that a pointless edit to a poor post is only going to net more down votes from the community.