The +1 refers to number of views. When you call up your statistics, you can get an idea of how many visits occurred to any specific article over various periods of time. I assume that if you have at least one view in the 30-day column and the work is already featured, the article will go automatically transfer to Discover HubPages. This hasn't been explained clearly by the staff, however.
As far as style, HP once told me they prefer American Psychological Association (APA) style, commonly used in research writing. Quality, as I understand it, depends on mechanics (spelling and grammar), organization, relevance of content (something readers will seek), and appearance (no unnecessary italics, bolds, underscores, asterisks, etc.). After that, the article's score goes up or down depending on actual traffic flow.
I've helped a number of writers with specific suggestions on all these quality goals. Some of them implement the suggestions; others not. I am neither part of the HP team, nor do I charge anything when I do this. I have found, however, that when the changes are made, the struggling author gets the article featured.
I hope I've answered your question.