In my opinion, if an edit improves a question in some way, and someone's willing to make it, they should feel free to make the change. Whether this is fixing a typo or retagging the question, the accumulation of all these tiny improvements will lead to a higher quality post, and a higher quality site.
I also think that, the majority of the time, a question's title should also be a question, as it helps the person asking the question to identify the core focus of their problem, which in turn helps the people looking at the recent questions list get a better idea of what the questions in the list are asking. For people with the same problem in the future, the similar questions search in the "Ask Question" page is based off question titles, and the title is placed in the
<title> of the page, which is given additional weight in a Google search. Finally, having the majority of the posts on the site phrased in the form of a question serves to improve consistency, as well as to serve as an example to new users of how to ask their questions.
That said, simply changing "How to" to "How do I" long after the question is asked and answered really only serves that last point as it didn't help the asker, the answerers, and provides no additional keywords for searchers. Still, I don't think that anyone's arguing that changing the title is bad if there's other stuff that needs to be changed in the body and tags of the question as well, which indicates that an edit that changes the title from "How to" to "How do I", taken by itself, is at least not a negative.
The point of contention comes with the fact that there's also a 'cost' to each edit - every time a question or answer is edited it's put back at the top of the active queue, the default sort order for the front page. If lots of edits are done in quick succession, they drowned out the actual open questions making it harder to get questions answered, and to find questions to be answered.
The correct solution to this, in my opinion, is to build in support for non-bumping edits into the system. Wikipedia is a good example here - nobody gets chastised for fixing typos, and there's a way to mark edits as 'minor', indicating that the edit does not change the content and does not need to reviewed.
Barring that, however, I agree that edits to older posts should be done no more than a few at a time, and that it's better to use those edits to fix up the posts that really need it rather than to change something minor. I disagree, however, that any edit that improves the post should not be made because it's 'too minor'. The quantity and frequency of the edits is the problem, not the fact that they change comparatively little.